Macromolecular dispersion type liquid crystal display element and method of manufacturing the same

ABSTRACT

A method of forming a polymer dispersion type liquid crystal display element having a polymer dispersion type liquid crystal sandwiched between a pair of substrates, each having an inside electrode, is disclosed. The droplets either are dispersed and held in a continuous matrix phase of the polymer or held in a three dimensional network of a matrix containing the polymer. In the method, the value of (V90×R/d is at least 0.7 where V90 is that voltage required for transmittance of a voltage-transmittance characteristic of the display element to be 90% when the element is at 30° C., d is the interval between the substrate pair, and R is the average particle size of the liquid crystal droplets. In the method, a liquid crystal polymer precursor compatible solution containing a liquid crystal and a polymer precursor placed between the substrate pair is held at a temperature greater than the thermal phase separation temperature of the precursor solution, which is irradiated with ultraviolet to permit phase separation of the liquid crystal and the polymer precursor.

This is a Continuation of application Ser. No. 09/068,451 filed May 8,1998 now abandoned, which is a 371 of PCT/JP97/03266 filed Sep. 16,1997.

TECHNICAL FIELD

The present invention relates to a liquid crystal display element and,more particularly, to a polymer dispersion type liquid crystal displayelement in which liquid crystals are dispersed in polymer. The polymerdispersion type liquid crystal according to the present inventionincludes both of polymer dispersion type liquid crystal in a narrowsense in which liquid crystal droplets are dispersed and held in acontinuous phase in a polymer matrix and the so-called polymer networkliquid crystal in which liquid crystal droplets are dispersed and heldin networks of polymer matrix in the form of a three dimensionalnetwork.

BACKGROUND ART

The liquid crystal display element, which is a display element featuringlow profile, lightweight and low power consumption, has been widely usedas a display screen of word processors and of TVs hitherto. Of the knownliquid crystal display elements, the polymer dispersion type liquidcrystal display element using light-scattering mode, which requires nopolarizers and also requires no alignment layer treatment to substrates,enables a simplified structure and bright and good contrast ratiodisplay. In particular, when the polymer dispersion type liquid crystaldisplay element is applied to projection type liquid crystal displayadapted to project images on the screen, a large image of bright andexcellent contrast ratio can be easily created on the screen, andaccordingly the use of the polymer dispersion type liquid crystaldisplay element in this field is being progressing.

The polymer dispersion type display element has however a delay indevelopment, as compared with the liquid crystal display elements of TN(Twisted Nematic) mode and STN (Super Twisted Nematic) mode and stillhas the following disadvantages. Since the polymer dispersion typeliquid crystal is such that microscopic liquid crystal droplets ofmicron order are confined in the polymer matrix, liquid crystalmolecules in the liquid crystal droplets are affected by physicalrestrictive force (hereinafter it is called as “anchoring”) from aninterfacial boundary of the polymer matrix. Because of this, the polymerdispersion type liquid crystal display element is poorer in response ofthe liquid crystal molecules to electric field than other types ofliquid crystal display elements and has a hysteresis that creates adifference in transmittance of the element between at a raised voltageand at a dropped voltage. Further, since the anchoring strength variesdepending on temperature of the element, as ambient temperature aroundthe element varies, the transmittance characteristics of the elementrelevant to the response to electric field and to driving voltage varyconsiderably. Due to this, although the polymer dispersion type liquidcrystal display element holds promise as the coming generation liquidcrystal display element, the element of high reliability withsatisfactory performance have not yet been realized in the presentcircumstances.

Following techniques for the polymer dispersion type liquid crystaldisplay element have been hitherto disclosed.

(1) Disclosed by Flat Panel Display '91, on page 221, published byNIKKEI BP and others is the technique according to which after acompatible mixture of a liquid crystal material and polymerizablemonomer is injected in between two opposing substrates, the compatiblemixture is irradiated with ultraviolet from above of the substratesunder a given temperature condition, to polymerize the monomer whilephase separation of the liquid crystal is produced, to thereby producethe polymer dispersion type liquid crystal in which liquid crystals aredispersed in polymer matrix or are dispersed with continuously linked toeach other.

(2) Disclosed by Japanese Laid-open Patent Publication No. Hei5(1993)-158020 is the technique of controlling phase separation byconcentration of polymerization initiator in the liquid-crystal-polymermixture, polymerization temperature and intensity of ultraviolet beingall controlled simultaneously.

(3) Disclosed by Japanese Laid-open Patent Publication No. Hei5(1993)-224180 is the technique of controlling a rate of polymerizationof monomers in the guest host type of polymer dispersion type liquidcrystal display element.

(4) Disclosed by Japanese Laid-open Patent Publication No. Hei5(1993)-158020 is the technique of improving intensity of ultravioletfrom a conventional range of about 10 mW/cm² (cf. Symposium on page 414of The 21^(st) Liquid Crystal Symposium by Mr. Fujikake and others, forexample) to the range of from 0.5 mW/cm² or more to 100 mW/cm² or less.

(5) Disclosed by Japanese Laid-open Patent Publication No. Hei5(1993)-127174 is the technique according to which intensity ofultraviolet is set to be 15 mW/cm² or more when a radical polymerizationinitiator is used, while on the other hand, the intensity of ultravioletis set to be in the range of from 100 mW/cm² or more to 150 mW/cm² orless when an ionic polymerization initiator is used.

(6) Disclosed by Japanese Laid-open Patent Publication No. Hei6(1994)-194629 is the technique on a surface temperature of a liquidcrystal panel irradiated with ultraviolet, according to whichpolymerization is produced under temperatures higher than thermal phaseseparation temperature by a minimum requiring extent, to allow forsolubility limit of liquid crystals.

However, these conventional techniques were not enough to solve theabovesaid problems satisfactorily and were also disadvantageous in thatit takes much time to accomplish the phase separation by, for example,irradiation of ultraviolet (it takes much time to solidify polymermatrix), due to which great variations in size of liquid crystaldroplets and interval between neighboring liquid crystal droplets arecaused. Also, the conventional techniques involve the problem that sincethe anchoring strength of interface liquid crystal/polymer is notadequately adjusted, the response to electric field is not sufficientand the optical hysteresis in high temperature range is as large as 3 to5% and also the optical hysteresis in low temperature range (less than10° C.) increases further.

At present, what is physical value that controls the optical hysteresisdirectly is not thoroughly clarified. For this reason, the measurementsto improve the optical hysteresis effectively have not yet been foundout.

DISCLOSURE OF THE INVENTION

The present invention as a group has been made in the light of thepresent circumstances described above. It is the primary object of thepresent invention to develop a new technique for determining opticalhysteresis precisely so that a polymer dispersion type liquid crystaldisplay element of improved optical hysteresis can be provided by theapplication of the new technique. It is the secondary object of thepresent invention to develop a technique for adjusting anchoringproperly to thereby provide a polymer dispersion type liquid crystaldisplay element with improved response to electric field and improvedoptical hysteresis. Further, it is the tertiary object of the presentinvention to provide an improved polymer dispersion type liquid crystaldisplay element based on the above-mentioned two objects.

It is noted that although the present invention as a group is on thebasis of the same or similar conception, since the each individualinvention is embodied into different examples, the present invention asa group is divided into the first inventive group; the second inventivegroup; the third inventive group; and the fourth inventive group forevery closely related invention in the specification. Hereinafter, thedescription on the content of the invention is given in sequence forevery group (inventive group).

According to the first inventive group, the relationship betweenmanufacturing conditions (polymerization temperature, intensity ofultraviolet and ultraviolet irradiation time) and optical hysteresis isdetermined, on the basis of which the optical hysteresis of the liquidcrystal display element is reduced.

The first inventive group comprises following aspects:

(1) A polymer dispersion type liquid crystal display element, in which apolymer dispersion type liquid crystal is sandwiched between a pair ofsubstrates each having an electrode at the inside thereof,

wherein said polymer dispersion type liquid crystal is such that liquidcrystal droplets are dispersed and held in a continuous phase of matrixcomprising polymer compound or are dispersed and held in networks of athree dimensional network form of matrix comprising polymer compound,and

wherein said liquid crystal droplets located in all areas except an areain the vicinity of interfaces between said substrates and said polymerdispersion type liquid crystal are substantially identical to each otherin shape and size.

(2) In the above described aspect (1), standard deviation in averageparticle size of said liquid crystal droplets is within the range of ±5%of a mean value.

(3) In the above described aspect (1) or (2), wherein said polymercompound comprises polymers including monofunctional acrylate and/ormultifunctional acrylate.

(4) In the above described aspect (3), said monofunctional acrylate isisostearyl acrylate; and said multifunctional acrylate is at least onematerial selected from the group consisting of triethylene glycoldiacrylate, PEG#200 diacrylate, PEG#400 diacrylate, neopentyl glycoldiacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate,pentaerythlytoltriacrylate, and bifunctional urethane acrylate expressedby the chemical formula 1 given below:

CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1

where n=an integer.

(5) A method for producing a polymer dispersion type liquid crystaldisplay element, said method comprising a phase separation step in whichafter a liquid crystal polymer precursor compatible solution includingliquid crystal and polymer precursor is placed between a pair ofsubstrates each having an electrode at the inside thereof, a surface ofsaid substrates is irradiated with ultraviolet so that said liquidcrystal and said polymer precursor in said liquid crystal polymerprecursor compatible solution can be phase-separated from each other andalso said polymer precursor can be polymerized and cured, to therebyproduce a polymer dispersion type liquid crystal in which liquid crystaldroplets are dispersed and held in a continuous phase of matrixcomprising polymer compound or are dispersed and held in networks of athree dimensional network form of matrix comprising polymer compound,said phase separation step comprising the step of controlling the time Tfrom initiation of the irradiation of ultraviolet until completion ofthe phase separation so that at least any one of a degree ofpolymerization of said polymer precursor of said liquid crystal polymerprecursor compatible solution, a rate of phase separation and agenerating density of liquid crystal nuclei separated can be controlledto even particle sizes of the liquid crystal droplets dispersed and heldin said matrix.

(6) In the above described aspect (5), where T1 is the time from saidirradiation of ultraviolet until the initiation of phase separation ofsaid liquid crystal polymer precursor compatible solution and T₁₀₋₉₀ isthe time required for a rate of progress of phase separation to changefrom 10% to 90% when the rate of progress of the phase separation forall liquid crystals to be separated from said liquid crystal polymerprecursor compatible solution is defined as 100%, the control of saidtime T is performed by controlling said time T1, said time T₁₀₋₉₀, orboth of said time T1 and T₁₀₋₉₀.

(7) In the above described aspect (5), temperature of said liquidcrystal polymer precursor compatible solution and intensity ofultraviolet with which said liquid crystal polymer precursor compatiblesolution is irradiated are controlled so that the relation ofT₁₀₋₉₀=a×T1+b (a, b are constants of a linear function) can hold betweensaid time T1 and said time T₁₀₋₉₀ and said a can be within the range offrom 0.4 or more to 0.7 or less.

(8) In the above described aspect (6), said time T1 is controlled to be5 seconds or less by controlling temperature of said liquid crystalpolymer precursor compatible solution and intensity of ultraviolet withwhich said liquid crystal polymer precursor compatible solution isirradiated.

(9) In the above described aspect (8), said intensity of ultraviolet isnot less than 100 mW/cm².

(10) In the above described aspect (8), said intensity of ultraviolet isnot less than 100 mW/cm² and also said temperature of said liquidcrystal polymer precursor compatible solution is higher than thermalphase separation temperature of said liquid crystal polymer precursorcompatible solution by 2 to 15° C.

(11) In the above described aspect (8), said intensity of ultraviolet isin the range of 160 mW/cm² to 400 mW/cm² and also said temperature ofsaid liquid crystal polymer precursor compatible solution is higher thanthermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 6 to 13° C.

(12) In the above described aspect (6), temperature of said liquidcrystal polymer precursor compatible solution and intensity ofultraviolet with which liquid crystal polymer precursor compatiblesolution is irradiated are controlled so that said time T₁₀₋₉₀ can be 6seconds or less.

(13) In the above described aspect (12), said intensity of ultravioletis not less than 100 mW/cm².

(14) In the above described aspect (12), said intensity of ultravioletis not less than 100 mW/cm² and also said temperature of said liquidcrystal polymer precursor compatible solution is higher than thermalphase separation temperature of said liquid crystal polymer precursorcompatible solution by 2 to 15° C.

(15) In the above described aspect (12), said intensity of ultravioletis in the range of 160 mW/cm² to 400 mW/cm² and also said temperature ofsaid liquid crystal polymer precursor compatible solution is higher thanthermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 6 to 13° C.

(16) In the above described aspect (6), said time T1 and said timeT₁₀₋₉₀ are controlled to be 5 seconds or less and 6 seconds or less,respectively, by controlling temperature of said liquid crystal polymerprecursor compatible solution and intensity of ultraviolet with whichsaid liquid crystal polymer precursor compatible solution is irradiated.

(17) In the above described aspect (5) or (16), said liquid crystalpolymer precursor compatible solution includes monofunctional acrylateand/or multifunctional acrylate.

(18) In the above described aspect (17), said monofunctional acrylate isisostearyl acrylate; and said multifunctional acrylate is at least onematerial selected from the group consisting of triethylene glycoldiacrylate, PEG#200 diacrylate, PEG#400 diacrylate, neopentyl glycoldiacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate,pentaerythlytoltriacrylate, and bifunctional urethane acrylate expressedby the chemical formula 1 given below:

CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1

where n=an integer.

Next, the significance of the constructions described above will bedescribed below.

Shown in FIG. 1 is an example of measured optical hysteresis (ambienttemperature of 30° C. when measured) of a conventional polymerdispersion type liquid crystal display element. In FIG. 1, a solid linerepresents a transmittance curve at a raised voltage (an applied voltageis gradually raised) and a broken line represents a transmittance curveat a dropped voltage (an applied voltage is gradually dropped). As shownin FIG. 1, a general type of polymer dispersion type liquid crystaldisplay element has a strong optical hysteresis. The term of “opticalhysteresis” used herein is intended to mean the property of causing adifference in transmittance between in the process of the voltage beingraised and in the process of the voltage being dropped when the samevoltage is applied, and the magnitude is represented by percentage forluminance of white level.

Incidentally, in the polymer dispersion type liquid crystal, there aretwo orientation patterns of liquid crystal molecules in the liquidcrystal droplets to be oriented in the direction of the major axes (Sov.Phys. JETP58(6), December 1983). One of the orientation patters is thebipolar form having two poles. In the bipolar-form orientation pattern,each liquid crystal molecule in the droplet is oriented toward twopoles, with the major axis being in parallel to the interfacial boundary(spherical surface). Another one is the radial form. In the radial-formorientation pattern, a single pole (point defect) exists in the vicinityof the center of liquid crystal droplet and each liquid crystal moleculein the droplet is oriented in the radial direction, with one end of themajor axis oriented toward said single pole and the other oriented tothe spherical surface.

In general, the polymer dispersion type liquid crystal display elementexhibits strong optical hysteresis in the relation to operatingtemperature. The origin of this hysteresis effect will be examined inassociation with the orientation patterns mentioned above. It is knownthat the polymer dispersion type liquid crystal display element has atendency of the optical hysteresis increasing excessively attemperatures lower than a certain temperature. The origin is thought tobe due to the transition of the orientation pattern of the liquidcrystal molecules from the bipolar form to the radial form whentemperature of the element becomes lower than a certain temperature.Also, it is thought that the primary origin of the optical hysteresiscaused when the temperature for the bipolar-form orientation pattern tobe produced exceeds the certain temperature is due to displacement ofthe poles in the bipolar-form orientation pattern or disappearance ofthe poles being caused by variations in applied voltage (e.g. LiquidCrystal Dispersions written by P. S. Drzaic at page 269, WorldScientific 1996). On the other hand, in the radial-form orientationpattern of liquid crystals, there inevitably exist some liquid crystalmolecules orienting in a direction perpendicular to the substrates whileno voltage is applied as well. Due to this, in the polymer dispersiontype liquid crystal element in which liquid crystal molecularorientation is controlled to make the switching between scatteringcondition and permeation, the liquid crystal droplets are required totake the bipolar-form orientation pattern, from the view point ofcontrast.

In short, reduction of the optical hysteresis requires that the liquidcrystal molecules take the bipolar-form orientation pattern and also thebipolar-form orientation pattern is stably maintained in an operatingtemperature range of the liquid crystal display element (a drivingtemperature range of the element). As illustrated in the experimentsdiscussed later, the inventors found out the fact that generation oforiented poles and transition of the poles caused by the application ofvoltage are highly dependent on the shape of liquid crystal droplet anda magnitude of interfacial restrictive force (anchoring) of the polymersurrounding the liquid crystal droplets.

Specifically, the more the form of the liquid crystal droplets nears toa low-distortion ellipsoid of revolution, the more the movement of thepoles decreases, whereby the orientation pattern is stabilized and theoptical hysteresis is reduced. In particular, when variability of theparticle size of the liquid crystal droplets is within the range of 10%,the optical hysteresis is reduced drastically. However, because ofwettability between the substrates and the liquid crystals, the liquidcrystal droplets in the vicinity of the substrates come intosemi-spherical in shape, with their great circle contacting with thesubstrates. It is thus difficult to control the shape of the liquidcrystal droplets contacting with the substrates, so the remaining liquidcrystal droplets except those contacting with the substrates should becontrolled to be formed into a substantial ellipsoid of revolution form.Also, as long as the liquid crystal droplets each have a substantialellipsoid of revolution, the liquid crystal droplets may be partiallylinked with another liquid crystal droplets.

The higher the percentage of the liquid crystal content in liquidcrystal polymer precursor compatible solution in preparation of thepolymer dispersion type liquid crystal, the more outstandingly theoptical hysteresis appears. This is a consequence of: with a higherpercentage of the liquid crystal content, the particle size of theliquid crystal droplets increases in general to facilitate distortion ofthe liquid crystal droplets, which in turn allows extra poles (more thantwo poles) to occur.

When the interfacial anchoring strength is weak, even if there exists anextra pole, since the extra pole other than the poles in the bipolarorientation is destroyed with the application of an electric field, theoptical hysteresis is weakened. However, any weak anchoring strength isnot always of desirable. This is because, in the case of significantlyweak anchoring strength, the liquid crystal molecules do not go back totheir original state even with de-energization of the applied voltage,which in turn makes it difficult to do the light-and-dark switching bythe control of the application of voltage. Therefore, the anchoringstrength must be adjusted to a proper strength. In general, the opticalhysteresis in the high temperature range is antinomic with that in thelow temperature range. There is the tendency that when the opticalhysteresis in the high temperature range is tried to be reduced, theoptical hysteresis in the low temperature range increases, and viseversa. Due to this, the prior arts have not succeeded in accomplishingthe polymer dispersion type liquid crystal display element having theoptical hysteresis which is capable to be reduced in a wide temperaturerange.

Next, the ways of reducing distortion of the liquid crystal droplets toadjust the form of the liquid crystal droplets will be described below.The first way is to accelerate a rate of polymerization of the polymerwhen phase separation and polymerization of the polymer are made byirradiation of ultraviolet to the liquid crystal polymer precursorcompatible solution.

Description on this will be given with reference to FIG. 2. FIG. 2schematically illustrates the forming states of liquid crystal droplets:FIG. 2(a) illustrates the form of the liquid crystal droplets in thecase of the rate of polymerization being fast (e.g. the rate ofpolymerization not more than 6 sec.) and FIG. 2(b) illustrates the formof the liquid crystal droplets in the case of the rate of polymerizationbeing slow (e.g. the rate of polymerization not less than 10 sec.). Withan accelerated rate of polymerization, the liquid crystal dropletseparating nuclei (microscopic liquid crystal droplets producedimmediately after the phase separation) are allowed to spread uniformly,which in turn can allow the separating nuclei to grow to liquid crystaldroplets within a short time. Consequently, neighboring liquid crystaldroplets are kept with properly spaced intervals from each other, andliquid crystal droplets with relatively uniform form are formed. On theother hand, with a decelerated rate of polymerization, it take lots oftime until completion of polymerization, which can allow other liquidcrystal droplets to squeeze in spaces between the neighboring liquidcrystals in stages of growth of the liquid crystal droplets, to causemutual forms of the droplets to be distorted and thereby form liquidcrystal droplets of uneven in shape. In addition, with the deceleratedrate of polymerization, excessively large liquid crystal droplets can beproduced. As discussed later in detail, the rate of polymerization ofthe polymer precursor can be controlled by adjusting temperature of theliquid crystal polymer precursor compatible solution (hereinafter it isreferred to as “polymerization temperature”) and intensity ofirradiation of ultraviolet (hereinafter it is simply referred to as“intensity of ultraviolet”) during the phase separation.

The second way is to adjust viscosity and hardness of the polymerprecursors surrounding the separating nuclei during the separation. Whenthe polymer precursors are low in degree of polymerization, theirviscosity is low and their hardness remains soft, so that the separatingnuclei are affected, during growth, by fluctuation of the liquid crystalpolymer precursor compatible solution and thus are liable to developinto a distorted form. On the other hand, when the separating nucleiseparate in a stage in the full development of polymerization of thepolymer precursors, the growth of the separating nuclei is restricted bythe polymer precursors high in viscosity and high in hardness (e.g.dimer or trimer), and the separating nuclei avoid high-hardness portionsof the polymer precursor, during growth. As a result of this, distortedliquid crystal droplets are formed.

It will be appreciated from the above that there exists an optimum rangein the degree of polymerization of the polymer precursors (whichcorresponds to the hardness of the polymer precursors) during a stage ofseparation of liquid crystals. It should be noted that the hardness ofthe polymer precursors can be adjusted, at the time of separation of theseparating nuclei, by either controlling the degree of thepolymerization of the polymer precursors properly or selecting type andcomposition of the polymer precursor properly.

The third way is to control a generating density of separating liquidcrystal nuclei in a proper manner. FIG. 3(a) is a schematic showing ofseparating liquid crystal nuclei of a high generating density and FIG.3(b) is a schematic showing of separating liquid crystal nuclei of a lowgenerating density. When the generating density of the nuclei isexcessively high, the separating nuclei contact or connect to each otherin the process of growth to cause distortion of the nuclei. On the otherhand, when the generating density of the nuclei is excessively low, theseparating nuclei matures into excessively large liquid crystaldroplets, while the number of liquid crystal droplets decrease, leadingto deterioration of scattering characteristics. For this reason, it isnecessary to limit the generating density of the nuclei of the liquidcrystal droplets to an optimum range. The generating density of thenuclei is dependent on factors such as polymerization temperature, arate of polymerization, degree of polymerization of polymer precursors,and intensity of ultraviolet. Hence, the generating density of theseparating nuclei can be controlled by adjusting the polymerizationtemperature and the intensity of irradiation of ultraviolet. Inaddition, the generating density can be also controlled by setting thecompositions of the liquid crystal polymer precursor compatible solutionproperly.

As described above, the adjustment of rate of polymerization, degree ofpolymerization and generating density of the separating nuclei can allowthe liquid crystal droplets to have uniform form and also allow theoptical hysteresis to be reduced. The factors above can be controlled byvarying the polymerization temperature and the intensity of ultraviolet.However, there is a few precedents for the study of the degree ofpolymerization and the rate of polymerization in the phase separationhaving been made. Among others, there is no precedent for the study ofthe optical hysteresis characteristics of the liquid crystal displayelement having been made from the viewpoints of rate of polymerization,degree of polymerization, and generating density of the separatingnuclei.

Accordingly, the inventors have introduced capacitance as a physicalvalue which reflects the behavior of liquid crystal molecules moredirectly in its relation with the applied voltage, developing thetechnique of estimating the rate of polymerization, the degree ofpolymerization and generating density of the separating nuclei by use ofthe capacitance. And, they have succeeded in forming the polymerdispersion type liquid crystal display element which displays lowoptical hysteresis in a wide temperature range, based on the resultsobtained by the developed technique. The liquid crystal display elementthus formed have performance which has never been accomplished byconventional techniques, specifically, stable display performance in awide temperature range.

The significance of capacitance as the physical value is describedbelow. When the liquid crystal polymer precursor compatible solutioninjected in between a pair of substrates (hereinafter they are referredto as “liquid crystal panel”) is irradiated with ultraviolet, with abias voltage being applied thereto, the separating liquid crystal nucleiare formed by phase separation, and at the same time as the form of theseparating nuclei, the liquid crystal molecules in the separating nucleirise in response to the bias voltage. Thus, the capacitance of theliquid crystal panel varies in response to the form of the separatingnuclei and the growth (which means increase in the amount of separatingliquid crystals). Hence, the proportion of separating liquid crystals(to the total separating amounts) at some point in the progress of phaseseparation can be grasped by measuring the capacitance in the progressof phase separation with increased time. As long as the liquid crystalpolymer precursor compatible solution is identical in composition andalso the polymerization temperature (temperature of liquid crystalpanel) is constant, the separation of liquid crystals in the phaseseparation is determined by the degree of progress of polymerization ofthe polymer precursors. Accordingly, the degree of progress ofpolymerization (the degree of polymerization) and the rate ofpolymerization can be found by estimating the proportion of separatingliquid crystal by the capacitance. Further, this will be specificallydescribed with reference to experiments.

(Experiment 1)

In Experiment 1, the significance of measuring the capacitance isexperimentally clarified. In this experiment, the liquid crystal panelsimilar to that prepared in Example 1-1 as described later (in whichliquid crystal polymer precursor compatible solution is filled), whichwas set at a temperature higher than thermal phase separationtemperature of the liquid crystal polymer precursor compatible solutionby 9° C., was irradiated with ultraviolet of intensity of 200 mW/cm², tomeasure the capacitance in the progress of phase separation. The methodsof adjusting the liquid crystal panel temperature, of measuring thecapacitance and of preparing the liquid crystal panel and other detailedconditions are described later, with reference to Example 1-1 of thefirst inventive group.

FIG. 4 shows the measurement results of the capacitance. As shown inFIG. 4, the capacitance did not change for a certain time (T1) from thestart of ultraviolet irradiation. After the passage of the certain time,the capacitance increased sharply and thereafter was kept stable in ahigh level. This result shows that after the passage of the certain time(T1), the phase separation started, from the point of which theseparating of the liquid crystals progressed rapidly. Additionally, thestabilized capacitance indicates the completion of the separating ofliquid crystals (the completion of polymerization of polymer).

As shown in FIG. 4, where the time from the irradiation before the startof phase separation is T1, the time from the start of phase separationbefore the completion thereof is T2, and the time required for thecapacitance to change from 10% to 90% is T₁₀₋₉₀, when the T2 isestimated by the T₁₀₋₉₀, the time T1 corresponds to the time from thestart of irradiation of ultraviolet before the start of phase separationand the time T₁₀₋₉₀ corresponds to the rate of polymerization. It is tobe noted that the reason for letting the time T2 be T₁₀₋₉₀, not T₀₋₁₀₀,is that letting T2=T₀₋₁₀₀ leads to increase in error of measurement.

In general, the intenser the intensity of ultraviolet, the faster therate of polymerization of a polymer precursor becomes. Accordingly, withincreasing intensity of ultraviolet, the time T1, T2, particularly thetime T2, shortens. In addition, the higher the compatible solutiontemperature (which is the panel temperature and the polymerizationtemperature) as compared with thermal phase separation temperature ofthe liquid crystal polymer precursor compatible solution, the morefrequently the phase separation does not occur until the polymerizationof the polymer precursor progresses to some extent. As a result, thetime T1 from after the start of irradiation of ultraviolet before thestart of phase separation lengthens. In other words, the lengtheningtime T1 means that polymerization of the polymer precursor is being inprogress before the phase separation starts, which in turn means that atthe time of separating of liquid crystals, the polymer precursor growsinto polymer such as dimer or trimer. Polymer is high in viscosity andin hardness, as compared with monomer, so that as the time T1 increases,the viscosity and hardness of the polymer precursor increase and thegenerating density of the separating liquid crystal nuclei decreases.This means that as the time T1 increases, deformed liquid crystaldroplets are easily produced increasingly, as mentioned above.

Further, there is a close relation between the polymerizationtemperature of liquid crystal polymer precursor compatible solution andthe rate of polymerization, also. The higher the polymerizationtemperature, the longer the time T2 becomes.

It will be understood from the above that the measurements of the timeT1 and T2 enable a desirable phase separation condition for forming thewell-formed liquid crystal droplets to be determined, in associationwith the intensity of ultraviolet and the liquid crystal paneltemperature (polymerization temperature).

(Experiment 2)

In Experiment 2, the relationship between the degree of polymerization(viscosity.hardness) of the polymer precursor and the degree ofdeformation of the liquid crystal droplets (the factor on which theoptical hysteresis is dependent), the relationship between the intensityof ultraviolet and the optical hysteresis, and the relationship betweenthe intensity of ultraviolet and the optical hysteresis under thecondition of constant polymerization temperature are clarified. Otherconditions than the intensity of ultraviolet and the polymerizationtemperature are the same as those in the above Example 1, unlessotherwise specified.

First of all, the relationship between the polymerization temperatureand the optical hysteresis is described with reference to FIG. 5 (asconceptually illustrated). As already discussed, the polymerizationtemperature, close to the thermal phase separation temperature of liquidcrystal polymer precursor compatible solution, causes the phaseseparation easily, and as such can allow liquid crystal separatingnuclei to separate out in the polymer precursor low in the degree ofpolymerization As a result of this, although the generating density ofthe separating nuclei increases, since the viscosity.hardness of thepolymer precursor is low, the separating droplets are linked to eachother in the stage of growth to thereby produce the distorted liquidcrystal droplets. On the other hand, when the polymerization temperatureis high, the phase separation does not occur until he polymerization ofthe polymer precursor progresses to some extent. Thus, as a consequenceof the phase separation occurring at a stage of the polymerizationprogressing to some extent, the generating density of the separatingnuclei is reduced, and since the viscosity.hardness of the polymerprecursor around the separating nuclei is high, the liquid crystaldroplets are rendered prone to deformation. Thus, in either case, thepolymer dispersion type liquid crystal in which deformed liquid crystaldroplets are dispersed is formed, resulting in increase in opticalhysteresis. In view of the above, it is necessary to find out a properpolymerization temperature that enables the optical hysteresis todecrease.

FIG. 6 shows the measurement results of the optical hysteresis resultingfrom changes in the intensity of ultraviolet and the polymerizationtemperature for the liquid crystal panel (details are described later inExample 1-5). In this measuring experiment, the liquid crystal polymerprecursor compatible solution whose thermal phase separation temperatureis about 10° C. is used.

It will be understood from the result shown in FIG. 6 that at theintensity of ultraviolet of 110 mW/cm² (♦-♦), the lower thepolymerization temperature, the smaller the hysteresis becomes. It willbe also appreciated that at the intensity of ultraviolet of 200 mW/cm²,300 mW/cm², 400 mW/cm², and 550 mW/cm², there exist polymerizationtemperatures in which the optical hysteresis takes minimum values, andthere is a tendency that with increasing intensity of ultraviolet, thepolymerization temperatures coming to the minimum shift to highertemperatures. Further, the weaker the intensity of ultraviolet, thelarger the optical hysteresis. This means that the weak intensity ofultraviolet leads to decrease in the rate (progress speed) of phaseseparation after the start of phase separation, and the highpolymerization temperature leads to increase in the viscosity.hardnessand in turn leads to deceleration in the progress speed of the phaseseparation, so that, in any case, the distortion of the liquid crystaldroplets increases and resultantly the optical hysteresis increases.

In FIG. 6, the temperatures in which the optical hysteresis takes theminimum values range from 12° C. (at 110 mW/cm²) to 23° C. (at 400mW/cm² and 550 mW/cm²) in the polymerization temperature, with theminimum values ranging from 16° C. to 23° C. Also, it will be understoodthat the intensity of ultraviolet of not less than 200 mW/cm² isrequired for achieving the optical hysteresis of not more than 1%. It isnoted that the 23° C. is the temperature higher than the thermal phaseseparation temperature (10° C.) by 13° C.

Shown in FIG. 12 is the result of FIG. 6 presented by the connectionbetween the intensity of ultraviolet and the polymerization temperatureat which the optical hysteresis is reduced to the minimum. The liquidcrystal display element having small hysteresis can be obtained bysetting the polymerization temperature and the intensity of ultravioletproperly based on FIG. 12. However, it is preferable to set theintensity of ultraviolet to be in the range of 110 mW/cm² or more to 400mW/cm² or less, to allow for photodecomposition of the liquid crystalsas well as the optical hysteresis reduction effect in the lowtemperature range.

From the above result it is understood that the optical hysteresis canbe reduced significantly by selecting a temperature in the vicinity ofthe polymerization temperature in which the optical hysteresis isreduced to the minimum, according to the intensity of ultraviolet, toperform the phase separation.polymerization.

(Experiment 3)

In Experiment 3, the liquid crystal panels were prepared, with intensityof ultraviolet of 200 mW/cm² irradiated to the liquid crystal panels incommon but changes in the polymerization temperature only. The liquidcrystal panel thus prepared was measured in respect of the time T1 andthe time T2 in association with the polymerization temperature. Theremaining manufacturing conditions are the same as those of Example 1-1described later.

FIG. 7 shows the measurement results. As apparent from FIG. 7, withrising polymerization temperature, the time T1 and the time T2 bothgenerally lengthened. That the higher the polymerization temperature,the longer the time T1 means that the phase separation is started in astage in which the polymerization of polymer precursor is in progress.Also, the time T2 from the start of the phase separation to thecompletion of the phase separation lengthened more at higherpolymerization temperatures than at lower polymerization temperatures.That is presumed to be because the polymerization progressesconsiderably before the start of phase separation, to increase theviscosity, which resultantly retards the polymerization reaction afterthe start of the phase separation.

(Experiment 4)

Further, various kinds of elements were prepared, with thepolymerization temperature kept constant at 13° C. and with theremaining conditions being in common with those in the case of FIG. 6but changes in the intensity of ultraviolet only. The elements thusprepared were measured in respect of the connection between theintensity of ultraviolet and the optical hysteresis. The results areshown in FIG. 8. It is understood from FIG. 8 that at an increasingintensity of ultraviolet, the element can have reduced opticalhysteresis, and at the intensity of ultraviolet of 100 mW/cm² or more,the optical hysteresis is brought to 1.5% or less. In detail, at theintensity of ultraviolet of 200 mW/cm², for example, the opticalhysteresis is brought to about 1%, and at intensity of ultraviolet of300 mW/cm² and of 500 mW/cm², the optical hysteresis characteristics ofthe liquid crystal display elements are brought to about 0.8% and toabout 0.3%, respectively.

It is thought that the reason why at increasing intensity ofultraviolet, the optical hysteresis has a tendency to be reduced is thatwith increasing intensity of ultraviolet, the rate of polymerizationincreases to contribute rapid growth of the liquid crystal droplets, andas such can allow the liquid crystal droplets to be small in distortionand equal in size. To ensure this effect of the intensity ofultraviolet, T2 (equivalent to the rate of polymerization) which isdetermined by combination of the intensity of ultraviolet with thepolymerization temperature can be measured.

(Experiment 5)

In Experiment 5, the liquid crystal panels, prepared with variouschanges in the intensity of ultraviolet as well as in the polymerizationtemperature, were measured in respect of capacitance in the same manneras in Experiment 1, to determine the time T1 and the time T2 (the timeT2 defined by 10%-90%), on the basis of which the relationship betweenthe time T1 and the time T2 was clarified.

Shown in FIG. 9 are the measurement results in the relationship betweenthe time T2 and the optical hysteresis. From FIG. 9 it can be seen thatwhen the time T2 is 6 seconds or less, the optical hysteresis is broughtto about 2% or less; that when the time T2 is 4.5 seconds or less, theoptical hysteresis is brought to about 1.4% or less; and that the timeT2 is required to be set 2.5 seconds or less, in order to bring theoptical hysteresis to about 0.8% or less. It is also seen that the timeT2 is required to be set 1.5 seconds or less, in order to bring theoptical hysteresis to 0.5% or less.

Shown in FIG. 14 are the measurement results of Experiment 5 in therelationship between the time T1 and the time T2. It can be seen fromFIG. 14 that there is a generally regular correlation between the timeT1 and the time T2, so that they can make approximations with T2=a·T1+b(a, b are constants of a linear function). And, it became clear that thenumber a in the linear function has not so much dependence on theintensity of ultraviolet and is estimated to be 0.4 or more to 0.7 orless.

The results of FIG. 14 are thought to indicate that when the time T1from the start of irradiation of ultraviolet before the start of phaseseparation is long, the polymerization of polymer precursor progressesbefore the start of phase separation, which allows the solution toincrease in viscosity and in hardness, with the result that the time T2(the rate of polymerization) is rendered slow.

The rate of polymerization can be regulated also by changing thecomposition of the polymer precursor compositions including an additiveby addition of a polymerization promoter, for example.

The inventors confirmed that the rate of phase separation was changed byforming an insulation layer at the interface of the substrate. That isthought to be because the liquid crystals separated out in the vicinityof the interface of the substrate are affected by surface tension of thesubstrate. The larger the surface tension to the liquid crystals, thesooner the liquid crystals are separated out from the compatiblesolution.

(2) 2nd Inventive Group

It is the primary object of the invention of the second inventive groupthat the relation of manufacturing conditions for the phase separationof polymer dispersion type liquid crystals (polymerization temperature,intensity of ultraviolet and ultraviolet irradiation time) with particlesize of the liquid crystal droplets, orientation transition temperatureof the liquid crystal molecules, tilt angles of the liquid crystalmolecules and anchoring strength and the relationship between these andthe optical hysteresis are determined, on the basis of which the opticalhysteresis of the liquid crystal display element is reduced drasticallyin the operating temperature range of the liquid crystal display element(temperature of the element during driving), in a low temperature inparticular, to thereby produce a satisfactory display performance of theliquid crystal display element.

In the second inventive group, the anchoring index defined by thefollowing expression 2-1 is introduced as an index to estimate amagnitude of the anchoring strength, for making use of the anchoringindex.

Anchoring index=(V90×R)/d  Expression 2-1,

where

V90: an applied voltage required for the transmittance to become 90% inthe temperature of element of 30° C.;

d (μm): an interval between the substrates; and

R (μm): an average particle size of a liquid crystal droplet an averageinterval of a three dimensional network form of matrix comprisingpolymer compound.

The second inventive group comprises the following aspects.

(19) A polymer dispersion type liquid crystal display element in which apolymer dispersion type liquid crystal is sandwiched between a pair ofsubstrates each having an electrode at the inside thereof,

wherein said polymer dispersion type liquid crystal is such that liquidcrystal droplets are dispersed and held in a continuous phase of matrixcomprising polymer compound or are dispersed and held in networks of athree dimensional network form of matrix comprising polymer compound,

wherein liquid crystal molecules in said liquid crystal droplets presenta bipolar-form orientation pattern having at least two poles in thevicinity of interfaces between said liquid crystal droplets and saidpolymer compound, while no voltage is applied to said electrodes, and

wherein, where a clear point transition temperature of said liquidcrystal is let be Tni, said bipolar-form orientation pattern ismaintained at least when an operating temperature of the element fallsin the range of from 5° C. to (Tni−5)° C.

(20) In the above described aspect (19), tilt angles of said liquidcrystal molecules, in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, to said interfaces are notmore than 10 degrees, while no voltage is applied to said electrodes.

(21) In the above described aspect (19), said bipolar-form orientationpattern is maintained under an operating temperature of said elementfalling in the range of from 0° C. to (Tni−5)° C.

(22) In the above described aspect (21), tilt angles of said liquidcrystal molecules, in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, to said interfaces are notmore than 10 degrees, while no voltage is applied to said electrodes.

(23) In the above described aspect (19), said bipolar-form orientationpattern is maintained under an operating temperature of said elementfalling in the range of from −5° C. to (Tni−5)° C.

(24) In the above aspect (23), tilt angles of said liquid crystalmolecules, in the vicinity of interfaces between said liquid crystaldroplets and said polymer compound, to said interfaces are not more than10 degrees, while no voltage is applied to said electrodes.

(25) In the above aspect (19), said liquid crystal droplets located inall areas except an area in the vicinity of interfaces between saidsubstrates and said polymer dispersion type liquid crystal aresubstantially identical to each other in shape and size.

(26) In the above aspect (25), variations in size of said liquid crystaldroplets are within 10%.

(27) In the above aspect (19), said liquid crystal droplets located inall areas except an area in the vicinity of interfaces between saidsubstrates and said polymer dispersion type liquid crystal aresubstantially identical to each other in shape and size, and whereintilt angles of said liquid crystal molecules, in the vicinity ofinterfaces between said liquid crystal droplets and said polymercompound, to said interfaces are not more than 10 degrees, while novoltage is applied to said electrodes.

(28) In the above aspects (19) to (27), said polymer compound comprisespolymers including monofunctional acrylate and/or multifunctionalacrylate.

(29) In the above described aspect (28), said monofunctional acrylate isisostearyl acrylate; and said multifunctional acrylate is at least onematerial selected from the group consisting of triethylene glycoldiacrylate, PEG#200 diacrylate, PEG#400 diacrylate, neopentyl glycoldiacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate,pentaerythlytoltriacrylate, and bifunctional urethane acrylate expressedby the chemical formula 1 given below:

CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1

where n=an integer.

(30) A polymer dispersion type liquid crystal display element in which apolymer dispersion type liquid crystal is sandwiched between a pair ofsubstrates each having an electrode at the inside thereof,

wherein said polymer dispersion type liquid crystal is such that liquidcrystal droplets are dispersed and held in a continuous phase of matrixcomprising polymer compound or are dispersed and held in networks of athree dimensional network form of matrix comprising polymer compound,and

wherein a value of (V90 (volt)×R)/d is 0.7 or more, where V90 is anapplied voltage required for transmittance of a voltage.transmittancecharacteristic of said polymer dispersion type liquid crystal displayelement to become 90% under 30° C. of the temperature of element; d (μm)is an interval between said pair of substrates; and R (μm) is an averageparticle size of said liquid crystal droplets.

(31) In the above described aspect (28), liquid crystal molecules insaid liquid crystal droplets present a bipolar-form orientation patternhaving at least two poles in the vicinity of interfaces between saidliquid crystal droplets and said polymer compound.

(32) In the above described aspect (31), tilt angles of said liquidcrystal molecules, in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, to said interfaces are notmore than 10 degrees, while no voltage is applied to said electrodes.

(33) In the above described aspect (31), a clear point transitiontemperature of said liquid crystal is let be Tni, said bipolar-formorientation pattern is maintained at least when operating temperature ofsaid element falls in the range of from 5° C. to (Tni−5)° C.

(34) In the above described aspect (33), tilt angles of said liquidcrystal molecules, in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, to said interfaces are notmore than 10 degrees, while no voltage is applied to said electrodes.

(35) In the above described aspect (30), where a clear point transitiontemperature of said liquid crystal is let be Tni, said bipolar-formorientation pattern is maintained at least when an operating temperatureof said element falls in the range of from 0° C. to (Tni−5)° C.

(36) In the above described aspect (35), tilt angles of said liquidcrystal molecules, in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, to said interfaces are notmore than 10 degrees, while no voltage is applied to said electrodes.

(37) In the above described aspect (31), where a clear point transitiontemperature of said liquid crystal is let be Tni, said bipolar-formorientation pattern is maintained when an operating temperature of saidelement falls in the range of from −5° C. to (Tni−5)° C.

(38) In the above described aspect (37), tilt angles of said liquidcrystal molecules, in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, to said interfaces are notmore than 10 degrees, while no voltage is applied to said electrodes.

(39) A method for producing a polymer dispersion type liquid crystaldisplay element, said method comprising the phase separation step inwhich after a liquid crystal polymer precursor compatible solutionincluding liquid crystal and polymer precursor is placed between a pairof substrates each having an electrode at the inside thereof, saidsubstrates is irradiated on their surface with ultraviolet so that saidliquid crystal and said polymer precursor in said liquid crystal polymerprecursor compatible solution can be phase-separated from each other tothereby produce a polymer dispersion type liquid crystal in which liquidcrystal droplets are dispersed and held in a polymer matrix, whereintemperature of said liquid crystal polymer precursor compatible solutionat the time of said irradiation of ultraviolet is rendered higher than athermal phase separation temperature of said liquid crystal polymerprecursor compatible solution.

(40) In the above described aspect (39), said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 2 to 15° C.

(41) In the above described aspect (39), intensity of ultravioletirradiation is set to be not less than 160 mW/cm².

(42) In the above described aspect (39), said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 6 to 13° C. and also said intensity ofultraviolet irradiation is set at 160 mW/cm² to 400 mW/cm².

(43) A method for producing a polymer dispersion type liquid crystaldisplay element in which a polymer dispersion type liquid crystal issandwiched between a pair of substrates each having an electrode at theinside thereof, said polymer dispersion type liquid crystal being suchthat liquid crystal droplets are dispersed and held in a continuousphase of matrix comprising polymer compound or are dispersed and held innetworks of a three dimensional network form of matrix comprisingpolymer compound, wherein liquid crystal molecules in said liquidcrystal droplets present a bipolar-form orientation pattern having atleast two poles in the vicinity of interfaces between said liquidcrystal droplets and said polymer compound, while no voltage is appliedto said electrodes, and wherein, where a clear point transitiontemperature of said liquid crystal used in said polymer dispersion typeliquid crystal display element is let be Tni, said bipolar-formorientation pattern is maintained under an operating temperature of saidelement falling in the range of from 5° C. to (Tni−5)° C., said methodcomprising the step that under the condition that said liquid crystalpolymer precursor compatible solution including liquid crystal andpolymer precursor placed between said pair of substrates is kept at ahigher temperature than a thermal phase separation temperature of saidliquid crystal polymer precursor compatible solution, said liquidcrystal polymer precursor compatible solution is irradiate withultraviolet to allow said liquid crystal and said polymer compound to bephase-separated from each other.

(44) In the above described aspect (39), said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 2 to 15° C. and also said intensity ofultraviolet irradiation is set at not less than 100 mW/cm².

(45) In the above described aspect (43), said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 6 to 13° C. and also said intensity ofultraviolet irradiation is set at 160 mW/cm² to 400 mW/cm².

(46) In the above described aspects (39) to (45), said liquid crystalpolymer precursor compatible solution includes monofunctional acrylateand/or multifunctional acrylate.

(47) In the above described aspect (46), said monofunctional acrylate isisostearyl acrylate; and said multifunctional acrylate is at least onematerial selected from the group consisting of triethylene glycoldiacrylate, PEG#200 diacrylate, PEG#400 diacrylate, neopentyl glycoldiacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate,pentaerythlytoltriacrylate, and bifunctional urethane acrylate expressedby the chemical formula 1 given below:

CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1

where n=an integer.

(48) A method for producing a polymer dispersion type liquid crystaldisplay element in which a polymer dispersion type liquid crystal issandwiched between a pair of substrates each having an electrode at theinside thereof, said polymer dispersion type liquid crystal being suchthat liquid crystal droplets are dispersed and held in a continuousphase of matrix comprising polymer compound or are dispersed and held innetworks of a three dimensional network form of matrix comprisingpolymer compound, wherein a value of (V90×R)/d is 0.7 or more, where V90is an applied voltage required for transmittance of a voltage *transmittance characteristic of said polymer dispersion type liquidcrystal display element to become 90% under 30° C. of the temperature ofelement; d is an interval between said pair of substrates; and R is anaverage particle size of said liquid crystal droplets, said methodcomprising the step that under the condition that said liquid crystalpolymer precursor compatible solution including liquid crystal andpolymer precursor placed between said pair of substrates is maintainedat a higher temperature than a thermal phase separation temperature ofsaid liquid crystal polymer precursor compatible solution, said liquidcrystal polymer precursor compatible solution is irradiate withultraviolet to allow said liquid crystal and said polymer precursor tobe phase-separated from each other.

(49) In the above described aspect (48), said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 2 to 15° C. and also said intensity ofultraviolet irradiation is set at not less than 100 mW/cm².

(50) In the above described aspect (48), said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 6 to 13° C. and also said intensity ofultraviolet irradiation is set at 160 mW/cm² to 400 mW/cm².

(51) In the above described aspects (48) to (50), said liquid crystalpolymer precursor compatible solution includes monofunctional acrylateand/or multifunctional acrylate.

(52) In the above described aspect (51), said monofunctional acrylate isisostearyl acrylate; and said multifunctional acrylate is at least onematerial selected from the group consisting of triethylene glycoldiacrylate, PEG#200 diacrylate, PEG#400 diacrylate, neopentyl glycoldiacrylate, 1,6-hexandiol diacrylate, trimethylolpropane triacrylate,pentaerythlytoltriacrylate, and bifunctional urethane acrylate expressedby the chemical formula 1 given below:

 CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1

where n=an integer.

(53) A polymer dispersion type liquid crystal display element in which apolymer dispersion type liquid crystal is sandwiched between a pair ofsubstrates each having an electrode at the inside thereof, said polymerdispersion type liquid crystal being such that liquid crystal dropletsare dispersed and held in a continuous phase of matrix comprisingpolymer compound or are dispersed and held in networks of a threedimensional network form of matrix comprising polymer compound, whereinsaid polymer dispersion type liquid crystal display element is soconstructed that when capacitance ratio of said element is defined byExpression 3-3 given below, said capacitance ratio becomes 60% or morefor a voltage required for light transmittance of said element to become10% or more:

Capacitance ratio=(capacitance for the case of any selected voltagebeing applied to the element/a maximum capacitance for the appliedvoltage)×100  Expression 3-3

(54) In the above described aspect (53), said maximum applied voltage is10V or more.

Next, the significance of the constructions described above will bedescribed below.

As described above, the inventors measured the electro-opticalcharacteristics caused by the change in the orientation pattern in thepolymer matrix and discovered the phenomenon that the optical hysteresisincreases when the liquid crystals are transformed from the bipolar-formorientation pattern to the radial-form orientation pattern in lowtemperature. Accordingly, the transition to the radial-form orientationpattern is suppressed in relatively low temperatures as well, in otherwords, the orientation pattern of the liquid crystals is allowed to besubstantially invariable within the operating temperature range of theliquid crystal display element, whereby the optical hysteresis can bedrastically reduced particularly in low temperatures to accomplish asatisfactory display performance in a wide temperature range.

A mechanism for the transition of orientation to be caused is brieflydescribed below, before the description on the suppression of thetransition of orientation pattern is given.

The liquid crystal molecules at their interfaces with the polymer areoriented with given tilt angles under relatively high temperatures,while on the other hand, they are oriented with their orienting verticalto the interfaces at low temperatures. Incidentally, the orientationpattern of the liquid crystal molecules in the polymer matrix of thepolymer dispersion type liquid crystal display element, in which liquidcrystals are dispersed in the polymer, is strongly dependent on theorientation of the liquid crystal molecules at their interfaces with thepolymer. In other words, the liquid crystals in the polymer matrix takeon an orientation pattern in which elastic energy, including potentialenergy, of the liquid crystal molecules at the interfaces assumes aminimum. Accordingly, under relatively high temperatures, the liquidcrystal molecules inside of the liquid crystal droplets take on theorientation determined by this nature, resulting in the bipolar-formorientation pattern.

On the other hand, with decreasing temperature, there arises thetransition to the radial-form orientation pattern.

The inventors found out that the above-described orientation transitiontemperature is dependent on anchoring strength in the interfaces betweenthe polymer and the liquid crystals, and as such can allow theorientation transition temperature to decrease by increasing theanchoring strength. It seems that that is because orientation of theliquid crystal molecules at the interfaces of the polymer and the liquidcrystal adjoining each other is determined by the anchoring strength atthe interfaces, so that, when the anchoring strength is weak, themolecular major axis of each liquid crystal molecule tends to rotateeasily, while on the other hand, when the anchoring strength is strong,the molecular major axis is strongly restrained by the interfaces andthus the liquid crystal molecules in the vicinity of the interfacialboundary tend to have difficulties in moving.

However, existing techniques have great difficulties in measuring theanchoring strength directly. Accordingly, the inventors introduced theabove-mentioned expression of (V90×R)/d as an anchoring index toestimate a magnitude of the anchoring strength, as mentioned above,where V90 (volt) is an applied voltage required for the transmittance tobecome 90% at temperature of element of 30° C.; d (μm) is an intervalbetween the substrates; and R (μm) is an average particle size of aliquid crystal droplet in polymer matrix, or an average interval of athree dimensional network form of matrix comprising polymer compound.

Specifically, suppose that the liquid crystal droplets having a particlesize of R are formed with linking with each other in the thicknessdirection of a pair of substrates spaced at an interval of d, the numberof liquid crystal droplets existing between the substrates can bedetermined by d/R. So, when V90 is divided by the d/R, that follows(V90×R)/d, which indicates an applied voltage per matrix when thetransmittance is 90%. Thus, the value of (V90×R)/d decreases when theanchoring strength of the interfaces is weak, and increases whenreverse. This is because the weaker the anchoring strength, the more theliquid crystal molecules tend to be oriented in the electric fielddirection with a smaller field intensity.

The measurement result on the correlation between the anchoring strengthand the orientation transition temperature is shown in FIG. 20. Thisproved that reduction of a lower limit of the operating temperaturerange to 10° C. or less requires (V90×R)/d≧0.7. Similarly, reduction ofa lower limit of the operating temperature range to 5° C. or lessrequires (V90×R)/d≧0.8, and reduction of a lower limit of the operatingtemperature range to 0° C. or less requires (V90×R)/d≧0.9. Thus, theliquid crystal display element responsive to a desired operatingtemperature range can be produced by controlling the anchoring index(anchoring strength). In particular, the polymer dispersion type liquidcrystal display element usable at lower temperatures than ever can beproduced by increasing the anchoring index.

Further, the inventors discovered that the anchoring strength isdependent on polymerization temperature of polymer during irradiation ofultraviolet and established the technique of setting the anchoringstrength at a desired value. In general, the liquid crystal displayelement is produced by the following. A liquid crystal panel, in whichcompatible material of polymer driver and liquid crystal is injected inbetween a pair of spaced apart opposing glass substrates, is kept at agiven temperature and is irradiated with ultraviolet, so as to allow theliquid crystals to separate by phase separation and also allow thepolymer driver to be polymerized. During the irradiation of ultraviolet,the liquid crystal panel was conventionally kept at the giventemperature which was substantially the same as the temperature for thephase separation to be generated. In contrast to this, when the liquidcrystal panel is irradiated with ultraviolet, with its kept at a certaintemperature slightly higher than the temperature for the phaseseparation to be generated, a phase separation line of the spinodaldecomposition which indicates a temperature condition for generation ofa phase separation is shifted toward higher temperature rapidly to allowthe phase separation to occur when the phase separation line reaches thetemperature of the liquid crystal panel. Thus, the anchoring strengthcan be set at any desired magnitude by controlling the above-describedcertain temperature (the temperature of the mixed solution of thepolymer driver and the liquid crystal) during the irradiation ofultraviolet.

The variations of the anchoring strength, depending on temperatures ofthe liquid crystal panel during the irradiation of ultraviolet, isthought to be due to the following. The degree of polymerization of thepolymer precursor around the liquid crystals separated by the phaseseparation varies in response to the temperature of the then liquidcrystal panel. As the configuration temperature rises, development ofthe polymer precursor into polymer increases and resultantly theviscosity increases. In addition, the viscosity is correlated with theanchoring strength, and as the viscosity increases, the anchoringstrength increases. Due to this, the anchoring strength is increased byrising the temperature of the liquid crystal panel during theirradiation of ultraviolet.

Thus, the transition temperature, in which the orientation pattern istransformed from the bipolar form to the radial form, is allowed todecrease by rising the temperature of the liquid crystal panel duringirradiation of ultraviolet in the process of manufacturing the liquidcrystal display element, and thereby the optical hysteresis at lowtemperatures can be reduced to obtain the liquid crystal display elementhaving good display performance in a wide temperature range.

It is noted that in excessively high temperatures, it takes long timefor polymerization, to lead to increase in particle size of the liquidcrystal droplets. In this case, if there is a scratch defect in theglass substrates, for example, due to variations in the degree ofseparation of the liquid crystals, variations in the particle size ofthe liquid crystal droplets are caused easily, so that there is apossible fear that an uniform display over the entire display screencannot be accomplished. Due to this, it is preferable that the liquidcrystal panel is irradiated with ultraviolet, with kept at a constanttemperature higher than the phase-separation-generation temperature by3-15° C. for example.

Also, it is preferable that the intensity of ultraviolet with which theliquid crystal panel is irradiated should be rendered higher than agiven intensity. This is because low intensity of ultraviolet causesdecreased rate of polymerization and in turn causes increased particlesize of the liquid crystal droplets, and accordingly there is a possiblefear of failing to realize the uniform display. Specifically, theultraviolet should be preferably irradiated at an intensity more than100 mW/cm², for example.

On the other hand, the transition temperature in which the orientationpattern is transformed from the bipolar form to the radial form can belowered also by allowing tilt angles of the liquid crystal molecules attheir interfaces with the polymer to decrease by adding an additive orequivalent. This is because, with decreasing tilt angles, the differencein energy between the bipolar-form orientation pattern and theradial-form orientation pattern increases and the bipolar-formorientation pattern is more stable in energy. Specifically, the tiltangles should be set to be 10° or less, preferably 5° or less to causehard transition to the radial-form orientation pattern.

(3) 3rd Inventive Group

In the third inventive group, the capacitance hysteresis Chys defined bythe following expression 3-1 and the optical hysteresis Thys defined bythe following expression 3-2 are newly introduced as indexes todetermine the optical hysteresis in association with the orientationpattern of the liquid crystal molecules, and with the aid of theseindexes, the liquid crystal display element small in the opticalhysteresis in the operating temperature range of the liquid crystaldisplay element (driving temperature of the element) is accomplished.Detailed description of the capacitance hysteresis Chys will be givenlater.

Capacitance hysteresis Chys=(C 2−C 1)/Cmax  Expression 3-1,

where C1: capacitance for any applied voltage V, in the process ofrising, of a voltage-capacitance characteristic;

C2: capacitance for any applied voltage V, in the process of dropping,of the voltage-capacitance characteristic; and

Cmax: capacitance for a maximum applied voltage of thevoltage-capacitance characteristic.

Optical hysteresis Thys=(T 2−T 1)/Tmax  Expression 3-2,

where

T1: intensity of transmitted light for any applied voltage V, which isin the process of rising, of the voltage-transmittance quantitycharacteristic;

T2: intensity of transmitted light for the applied voltage V, which isin the process of dropping, of the voltage-transmittance quantitycharacteristic; and

Tmax: intensity of transmitted light for a maximum applied voltage, ofthe voltage-transmittance quantity characteristic.

It is noted that the term used above, “a maximum applied voltage”, isintended to mean an applied voltage required for the liquid crystalmolecules to be fully oriented in the direction of electrical field.This voltage may be varied by variations in panel gap or the like. Ageneral type of polymer dispersion type liquid crystal display elementis so formed that a 10-15 volt is required for allowing the liquidcrystal molecules to be oriented in the direction of electrical field.

The third inventive group comprises the 55th-64th aspects describedbelow.

(55) A polymer dispersion type liquid crystal display element in which apolymer dispersion type liquid crystal is sandwiched between a pair ofsubstrates each having an electrode at the inside thereof, said polymerdispersion type liquid crystal being such that liquid crystal dropletsare dispersed and held in a continuous phase of matrix comprisingpolymer compound or are dispersed and held in networks of a threedimensional network form of matrix comprising polymer compound, wherein,when capacitance hysteresis in an operating temperature of said polymerdispersion type liquid crystal display element is defined byChys=(C2−C1)/Cmax, the Chys for any applied voltage V is 1.5% or less,where C1 is capacitance for any applied voltage V, which is in theprocess of rising, of a voltage-capacitance characteristic; C2 iscapacitance for the applied voltage in the process of dropping; and Cmaxis capacitance for the maximum applied voltage.

(56) In the above described aspect (55), where a clear point transitiontemperature of said liquid crystal is let be Tni, said Chys is 1.5% orless in operating temperatures of said element falling in the range offrom 5° C. to (Tni−5)° C.

(57) In the above described aspect (55), where a clear point transitiontemperature of said liquid crystal is let be Tni, said Chys is 1.5% orless in operating temperatures of said element falling in the range offrom 0° C. to (Tni−5)° C.

(58) In the above described aspect (55), where a clear point transitiontemperature of said liquid crystal is let be Tni, said Chys is 1.5% orless in operating temperatures of said element falling in the range offrom −5° C. to (Tni−5)° C.

(59) In the above described aspects (55) to (58), said maximum appliedvoltage is 10V or more.

(60) A polymer dispersion type liquid crystal display element in which apolymer dispersion type liquid crystal is sandwiched between a pair ofsubstrates each having an electrode at the inside thereof, said polymerdispersion type liquid crystal being such that liquid crystal dropletsare dispersed and held in a continuous phase of matrix comprisingpolymer compound or are dispersed and held in networks of a threedimensional network form of matrix comprising polymer compound, wherein,when optical hysteresis Thys in an operating temperature range of saidpolymer dispersion type liquid crystal display element is defined byThys=(P2−P1)/Pmax, where P1 is intensity of transmitted light for an anyapplied voltage V, which is in the process of rising, of avoltage-transmittance quantity characteristic; P2 is intensity oftransmitted light for the applied voltage in the process of dropping;and Pmax is intensity of transmitted light for a maximum appliedvoltage, and further when capacitance hysteresis Chys in an operatingtemperature of said polymer dispersion type liquid crystal displayelement is defined by Chys=(C2−C1)/Cmax, where C1 is capacitance for anyapplied voltage V, which is in the process of rising, of avoltage-capacitance characteristic; C2 is capacitance for the appliedvoltage in the process of dropping; and Cmax is capacitance for themaximum applied voltage, the Chys for the applied voltage with whichsaid Thys is maximized is 0.6% or less.

(61) In the above described aspect (60), a clear point transitiontemperature of said liquid crystal is let be Tni, the value of said Chysis 0.6% or less in operating temperatures of said element falling in therange of from 5° C. to (Tni−5)° C.

(62) In the above described aspect (60), a clear point transitiontemperature of said liquid crystal is let be Tni, the value of said Chysis 0.6% or less in operating temperatures of said element falling in therange of from 0° C. to (Tni−5)° C.

(63) In the above described aspect (60), a clear point transitiontemperature of said liquid crystal is let be Tni, the value of said Chysis 0.6% or less in operating temperatures of said element falling in therange of from −5° C. to (Tni−5)° C.

(64) In the above described aspects (60) to (63), said maximum appliedvoltage is 10V or more.

Next, the significance of the constructions described above will bedescribed below.

In a general type of polymer dispersion type liquid crystal displayelement, liquid crystal molecules in the liquid crystal droplets areindividually oriented in different directions while no voltage isapplied to the element. Due to this, light incident on the element isscattered to produce the opaque state. On the other hand, when voltageis applied thereto, the liquid crystal molecules are oriented in thedirection perpendicular to the substrates, and as a result, light can betransmitted to produce the transparent state. In addition, anintermediate state between the scattering state and the transparentstate can be displayed by adjusting a level of the applied voltage.However, the polymer dispersion type liquid crystal have the opticalhysteresis caused by the interfacial restrictive force, as mentionedabove. This causes a difference between the transmittance in the processof voltage rise and the transmittance in the process of voltage dropeven at an identical level of voltage, and resultantly causes a problemof unstable display performance in a halftone, in particular.

The inventors tried to pursue the origins of the strong opticalhysteresis, particularly, of the optical hysteresis strengthened in thelow temperature range, in the polymer dispersion type liquid crystal.Though there is a precedent for the measurement of the opticalhysteresis (e.g. Society for information Display '92, Pages 575-578 byS. Niiyama, et. al.), there is no precedent for the optical hysteresismeasured in relation to the orientation pattern of the liquid crystalsin the polymer dispersion type liquid crystal. Accordingly, theinventors measured capacitance as a physical value, which reflects theorientation pattern of liquid crystals more directly than thetransmittance does, to establish the technique of estimating theorientation pattern of the liquid crystals by means of the capacitanceand realized the polymer dispersion type liquid crystal display elementcapable to reduce the optical hysteresis in a low temperature range,based on the information obtained by the established technique.

The capacitance is a physical value originating from anisotropy indielectric constant of the liquid crystal molecules, and so a magnitudeof the capacitance reflects the orientation pattern of the liquidcrystals directly. Therefore, the optical hysteresis originating fromthe shape and the orientation pattern of the liquid crystal droplets canbe determined in relation to the behaviors of the liquid crystalmolecules by gaining a knowledge of hysteresis in the capacitance(capacitance hysteresis). The optical hysteresis is a property thatappears as a result of various factors, including the anchoringstrength, the panel gap, and the dielectric constant, refractive indexand temperature of the liquid crystal, being intricately affected eachother.

The relationship between the optical hysteresis and the capacitancehysteresis is described below, based on the experimental results. Of theexperimental results described below, Experiment 1 is the same asEmbodiment 3-1 of the third inventive group discussed later, so thedetails such as measurement conditions, are shown in Embodiment 3-1.

[Experiment 1]

The measurement result on the transmittance and the capacitancehysteresis at the element temperature of 30° C. is shown in FIG. 22 inthe form of voltage-transmittance characteristics andvoltage-capacitance characteristics. It is seen from FIG. 22 that avoltage corresponding to the transmittance of 10% was 4.47V and thecapacitance ratio C % corresponding to the voltage was 60%.

The capacitance ratio indicates a value defined by the followingexpression 3-3.

Capacitance ratio C %=(C/Cmax)·100  Expression 3-3

where Cmax is a capacitance at a maximum applied voltage and C is acapacitance in any applied voltage.

In order to confirm whether the above results can be generalized or not,various kinds of elements different in the optical hysteresis wereprepared and were subjected to similar experiments. The experimentalconditions are described in Example 3-1 discussed later. Theexperimental result is shown in FIG. 27. It was confirmed in FIG. 27that the larger optical hysteresis the liquid crystal display elementhas, the smaller the capacitance ratio of a 10%-transmittance-providingvoltage. In detail, a 2% or less hysteresis requires that a capacitanceratio of the 10%-transmittance-providing voltage of thevoltage-transmittance characteristics be set 60% or more. Similarly, an1% or less optical hysteresis requires that a capacitance ratio of the10%-transmittance-providing voltage of the voltage-transmittancecharacteristics be set 66% or more.

It was proven by the above experimental results that the panel havingreduced optical hysteresis can be realized by specifying the value ofcapacitance hysteresis.

[Experiment 2]

FIG. 23 is a plot of the results of Experiment 1, laying off the valuesof applied voltages as abscissa and the capacitance hysteresis Chys andthe optical hysteresis Thys as ordinate, to indicate the voltage-Chyscharacteristics and the voltage-Thys characteristics. In this figure, amaximum of Chys is designated as Chys MAX; a maximum of Thys as ThysMax; and a value of Chys in the voltage in which the Thys reaches themaximum as Chys.Thys MAX.

It was understood from FID. 23 that the Chys peaks at a lower voltagethan the Thys and that the peak of the Chys is lower than that of theThys.

[Experiment 3]

In order to check for the correlation between the Thys and Chys MAX,various kinds of elements were prepared under the manufacturingconditions shown in TABLE 3-1 below and were measured with respect ofthe voltage-capacitance characteristics with driving temperature varied.The measurement result is shown in TABLE 3-2. Shown in FIG. 24(a) is ashowing of the measurement result plotted between the Thys (%) and theChys MAX (%), and shown in FIG. 24(b) is a showing of the same plottedbetween the Thys (%) and the Chys.Thys MAX (%).

TABLE 3-1 Composition of Liquid Marks Crystal Precursor UV IntensityPolymerization in FIG. 24 Compatible Solution mW/cm² Temperature ° C. 2 wt % of HDDA is 95 11 added (N.B.) X The same as 95 17 Example 3-1(N.B.) * The same as 95 21 Example 3-1 (N.B.) ▴ 2 wt % of FM108 is 95 11added (N.B.) ▪ The same as 20 11 Example 3-1 (N.B.) (N.B.) Adding thesame to compatible solution of Example 3-1; HDDA: KARARAD available fromNIPPON KAYAKU CO., LTD.; and Light Acrylate FM108 available fromKYOEISHA CHEMICAL CO., LTD..

TABLE 3-2 Measurement Temperature Marks in FIG. Hysteresis (ElementDriving Temperature)° C. 24 Characteristics 0 5 10 20 30 40 50  THys2.34 2.11 2.08 3.26 4.14 4.28 4.82 CHys MAX 1.78 1.68 1.70 2.07 2.362.32 1.97 X THys 38.2  15.6  3.84 0.98 1.49 1.58 1.99 Chys Max 14.6 7.4  3.0 1.22 1.49 1.72 1.35 * THys 20.0  5.96 1.87 1.68 2.50 1.84 3.0Chys MAX 8.10 2.99 1.40 1.30 1.64 1.58 1.45 ▴ THys — — 37.7 3.53 0.830.92 1.10 Chys Max — — 9.77 2.28 1.39 1.54 1.08 ▪ THys — — 39.6 2.741.74 2.16 2.60 Chys MAX — — 15.0 2.54 1.67 1.98 1.64

It was understood from FIG. 24 (a) that a not more than 2% Thys requiressetting the Chys MAX to be 1.5% or less, while a not more than 1% Thysrequires setting the Chys MAX to be 1.0% or less.

Shown in FIG. 24(b) is a showing of the Chys.Thys MAX, the capacitancehysteresis for a voltage required for the optical hysteresis to comes topeak. It is seen from FIG. 24(b) that there is a correlation between theoptical hysteresis and the magnitude of the capacitance hysteresis forthe applied voltage required for the optical hysteresis to become amaximum. This correlation indicates that the element having smalloptical hysteresis can be produced by allowing a peak (Thys MAX) of theoptical hysteresis and a peak (Chys MAX) of the capacitance hysteresisshown in FIG. 23(b) to be away from each other or by allowing the peakof the capacitance hysteresis to decrease. It can be also seen that anot more than 2% the optical hysteresis requires the capacitancehysteresis peaking at a voltage to be set to be about 0.6% or less, anda not more than 1% optical hysteresis requires the capacitancehysteresis to be set to be about 0.3% or less. The details of conditionsrequired for preparation are omitted, though the relationship betweenthe Thys % and the Chys MAX in a high optical hysteresis region and therelationship between the Thys % and the Chys.Thys MAX (%) are plotted ina similar manner to the above in FIG. 25(a) and FIG. 25(b),respectively. It was confirmed in these FIGS. also that there exists theabove-described correlation therebetween.

It is noted that the difference between the peak of the opticalhysteresis (Thys MAX) and the peak of the capacitance hysteresis (ChysMAX) is due to the following. The magnitude of capacitance is a physicalvalue which directly reflects the degree of rise of liquid crystalmolecules (the angle between the major axis of rising molecule and thesubstrate), whereas the transmittance is not in a one-to-onecorrespondence with the angle above. For example, even when the liquidcrystal molecules is raised slightly by application of voltage, thescattering of light is still maintained.

To secure the practical display performance requires the opticalhysteresis of the element to be set to be preferably 2% or less, morepreferably 1% or less. The reason therefor is that the element of a notmore than 2% optical hysteresis is usable as display elements, such asdata projections, mainly for displaying characters or letters, andfurther the element of a not more than 1% optical hysteresis ensuressufficient gray scale display performance so that it can be used todisplays for displaying images or equivalent.

As described above, the polymer dispersion type liquid crystal displayelement having small optical hysteresis can be surely produced byspecifying the capacitance hysteresis. In general, the magnitude of theoptical hysteresis varies depending on the temperature of element, so itis essential that the optical hysteresis is reduced in the temperaturerange in which the liquid crystal display element is worked (the drivingtemperature range of the element). Specifically, the element having anot more than 2% optical hysteresis in the temperature range of 10° C.to 80° C. is usable to projection type displays, and the element havingthe optical hysteresis of not more than 2% in the temperature range of−20° C. to 80° C. is usable as displays on board of automobiles orequivalent.

The optical hysteresis can be estimated by the degree of differencebetween the peaks, rather than by a value of the capacitance hysteresisat a peak of the optical hysteresis.

(4) 4th Inventive Group

According to this inventive group, attention is given to therelationship between a surface tension of a droplet-formed liquidcrystal of a liquid crystal optical element and a critical surfacetension of an insulating film or a polymer compound in the form of amatrix of liquid crystal droplets. The invention as this inventive groupaims to improve temperature dependency, a response-to-electric fieldcharacteristic, and the like, of the liquid crystal optical element byholding this relation within a given range.

Further, the invention aims to achieve the object by improving thematerial of the insulating film.

Furthermore, the invention aims to achieve the same object by selectingthe material of the polymer compound and to simultaneously provide themethod for producing an excellent liquid crystal optical element withefficiency.

The fourth inventive group comprises the 65th-118th aspects.

The 65^(th) aspect is characterized in that in a polymer dispersion typeliquid crystal display element in which a polymer.liquid crystal complexin which droplets of liquid crystal are dispersed in a polymer compoundis filled in a space between a pair of electrodes supported bysubstrates and covered with insulating films, surface tension γLC ofsaid liquid crystal and critical surface tension γP of said insulatingfilms meet the relation of Expression 4-1:

γLC−γP<0  Expression 4-1.

According to the 66^(th) aspect, in the above described aspect 65, saidsurface tension γLC of said liquid crystal and said critical surfacetension γP of said insulating films further meet the relation ofExpression 4-2:

−1·dyne/cm<γLC−γP  Expression 4-2.

The 67^(th) aspect is characterized in that in the above describedaspect 66, said polymer.liquid crystal complex has a value of γ, whichindicates steepness of a threshold of a scattering-transmittancecharacteristic, falling in the range of 1.95 to 2.25.

The 68^(th) aspect is characterized in that in a polymer dispersion typeliquid crystal display element in which a polymer.liquid crystal complexin which droplets of liquid crystal are dispersed in a polymer compoundis filled in a space between a pair of electrodes supported bysubstrates and covered with insulating films, surface tension γLC ofsaid liquid crystal and critical surface tension γP of said insulatingfilms meet the relation of Expression 4-3:

0<γLC−γP<1·dyne/cm  Expression 4-3.

The 69^(th) aspect is characterized in that in the above describedaspect 65, 66, 67 or 68, said insulating films are made of polyaminoacids, polyamino acid derivatives or proteins.

The 70^(th) aspect is characterized in that in a polymer dispersion typeliquid crystal display element in which a polymer.liquid crystal complexin which droplets of liquid crystal are dispersed in polymer compound isfilled in a space between a pair of electrodes supported by substratesand covered with insulating films, critical surface tension γP of saidpolymer compound and surface tension γLC of said liquid crystal meet therelation of Expression 4-4:

γP>γLC  Expression 4-4.

The 71^(st) aspect is characterized in that in the above describedaspect 70, said polymer compound is formed by polymerization ofpolymerizable monomer and polymerizable oligomer, and further at leastone of said polymerizable oligomer and said polymerizable monomer has apolar group.

The 72^(nd) aspect is characterized in that in the above describedaspect 71, said polar group is at least one group selected from thegroup consisting of a hydroxyl group, a carboxyl group and an iminogroup.

The 73^(rd) aspect is characterized in that in the above describedaspect 70, 71 or 72, said γP and said γLC meet the relation of anexpression 4-4 in a full temperature range (−10° C. to 60° C.) in actualoperation of the display element:

γP>γLC  Expression 4-4.

The 74^(th) aspect is characterized in a method of producing a polymerdispersion type liquid crystal display element comprising:

the filling step in which a polymer precursor.liquid crystal mixture,including a liquid crystal and a polymer precursor, from which a polymercompound which allows the relation of Expression 4-4 to hold betweensaid liquid crystal and said polymer compound is formed bypolymerization, is filled in a space between a pair of electrodessupported by substrates and covered with insulating films, and

the polymer.liquid crystal complex forming step in which said polymercompound in said polymer precursor.liquid crystal mixture, after filled,is polymerized to form said polymer compound which allows the relationof Expression 4-2 to hold, while also polymer.liquid crystal complex inwhich droplets of said liquid crystal are dispersed in the formedpolymer compound is formed:

γP>γLC  Expression 4-4,

where γP is critical surface tension of the polymer compound and γLC issurface tension of the liquid crystal.

The 75^(th) aspect is characterized in that in the above describedaspect 74, said polymer precursor to be treated in said filling step andsaid polymer precursor.liquid crystal complex forming step is composedof polymerizable monomer and polymerizable oligomer, and further atleast one of the polymerizable oligomer and the polymerizable monomerhas a polar group.

The 76^(th) aspect is characterized in that in the above describedaspect 75, said polar group is at least one group selected from thegroup consisting of a hydroxyl group, a carboxyl group and an iminogroup.

The 77^(th) aspect is characterized in that in the above describedaspect 74, 75 or 76, said polymerization in said polymer.liquid crystalcomplex forming step is produced by the method of said polymerprecursor.liquid crystal mixture placed between said pair of substratesbeing irradiated with ultraviolet.

Other aspects are characterized by any proper combination of the 65^(th)to 77^(th) aspects described above.

The significance of the above described constructions will be describedbelow.

Significance of the 65^(th) to 69^(th) Aspects

Of electro-optical characteristics of the general type liquid crystaldisplay elements, the most essential characteristic is ascattering-transmittance characteristic indicating the relationshipbetween the transmittance of light to vertical incident light and anapplied voltage. A lot of experiments the inventors made showed thatvalues of γ, which indicate steepness of the threshold characteristic ofthe scattering-transmittance characteristic, were related to thetemperature dependency and the response time of the polymer dispersiontype liquid crystal display element, and the inventors found out acertain relative criterion that the values of γ, at which optimaltemperature dependency and response time can be obtained, range fromabout 1.7 to about 2.3. It is noted that the value of γ used here is theone defined by γ=V90/V10 (volt) is a voltage required for thetransmittance of light of the liquid crystal display element to vary by10% and V90 (volt) is a voltage required for the transmittance of lightof the liquid crystal display element to vary by 90%, when the maximumtransmittance of light of the liquid crystal display element is set tobe 100%.

Further, it was also found out that the value of γ, which indicates thesteepness of the threshold characteristic of the liquid crystal displayelement, is related to a critical surface tension γP of an insulatingpaint film material and a surface tension γLC of a liquid crystal to beformed into liquid crystal droplets in the polymer dispersion typeliquid crystal, so that the value of γcan be controlled by adjusting themutual surface tensions. The term of “surface tension” used herein isintended to mean surface energy. The significance is specificallydescribed below.

FIG. 28 is a sectional view of a main structure, illustrated in asimplified manner, of the liquid crystal display element of the presentinvention. The liquid crystal display element of the invention is notessentially different from the conventional type one in the mechanicalstructure itself.

The polymer dispersion type liquid crystal display element in the65^(th) to 69^(th) aspects comprises, as shown in FIG. 28, a pair ofopposing, support substrates 411, 412 made of transparent glasses orcrystals and having inner surfaces on which transference electrodes 413of indium.tin oxide and insulating paint films 414 made of various kindsof insulating paint film materials described later and covering thetransference electrodes 413 are laminated; and polymer dispersion typeliquid crystal 417 which is filled in between the transferenceelectrodes 413 oppositely disposed with the insulating paint films 414confronting each other and in which droplets 416 of liquid crystal aredispersed in polymer compound 415. The surface tension γLC of the liquidcrystal and the critical surface tension γp of the insulating paintfilms 414 then meet any one of the requirements of γLC −γp<0(hereinafter it is called conditional expression {circle around (1)}),−1 dyne/cm<γLC−γp <1 dyne/cm (hereinafter it is called conditionalexpression {circle around (2)}) or −1 dyne/cm<γLC−γp<0 (hereinafter itis called conditional expression {circle around (3)}). The peripheriesof the element, not shown, are joined together by sealing membersproduced by curing acid anhydride curing epoxy resin reinforced by glassfiber, for example, so as to form a closed container formed in one pieceas a whole.

The value of γ, which indicates steepness of threshold characteristic ofthe scattering-transmittance characteristic which is a basicelectro-optical characteristic of the liquid crystal display element, iscontrolled in association with adjustment of the relation between thecritical surface tension γp of the insulating paint films 414 coveringthe transference electrodes 413 on the interior surfaces of the supportsubstrates 411, 412 and contacting with the polymer dispersion typeliquid crystal 417 and the surface tension γLC of the liquid crystal tobe formed into droplets 416 of liquid crystal in the polymer dispersiontype liquid crystal 417. It is thought that this is caused by thefollowing operation.

The provision of the insulating paint films 414 contacting with thepolymer dispersion type liquid crystal 417, and also the intervalbetween the pair of insulating paint films being as narrow as about 13μm, contribute to cause an interactive force, such as Van der Waalsforce or polarity-polarity interactive force, to work between theinsulating paint films and the liquid crystals. The interactive forcefurther exerts on the droplets 416 of the liquid crystal material in theinterior of the polymer dispersion type liquid crystal 417 apart fromthe surfaces of the insulating paint films 414.

The existence of this interactive force allows the interfacialrestrictive force acting on the liquid crystal droplets 416 from thepolymer matrix 415 (equivalent of a torque required for the transitionof orientation) to vary, which in turn allows the value of γ whichindicates steepness of a threshold level in the liquid crystal displayelement to vary. Then, when the value of γ of the liquid crystal displayelement vary, the temperature dependency of the interfacial restrictiveforce acting on the liquid crystal droplets 416 from the polymercompound 415 varies with reference to the interactive force applied fromthe insulating paint films 1. As a result of this, not only thetemperature dependency of the driving voltage, etc. but also theresponse time become optimal. It seems that under the circumstance underwhich the liquid crystal material is more prone to got wet by theinsulating paint films 414 due to the both being polarized, for example,the interactive force acting on the liquid crystal material from theinsulating paint films 414 increases in strength, and under thecircumstance, the temperature dependency is also more prone toimprovement.

Significance of the 70^(th) to 77^(th) Aspects

As for the relationship between the critical surface tension of thepolymer compound and the surface tension of the liquid crystal, when thecritical surface tension γP of the polymer compound and the surfacetension γLC of the liquid crystal meet the requirement of γP>γLC, theinterface polymer/liquid crystal becomes stable in energy and then theliquid crystal molecules (director) are oriented at small angles by thepolymer compound interfacial tension to produce the bipolar-formorientation shown in FIG. 41(1). The bipolar-form orientation patterncan allow the orientations of the liquid crystal molecules to be changedby less kinetic energy than the radial-form orientation pattern, so thatthe response to electric field (response time) through the on/off ofvoltage is improved and also the hysteresis is reduced.

Although the liquid crystal is easily affected electro-optically byvariations in temperature, since the γP>γLC provides surface energy ofthe polymer compound larger than the surface energy of the liquidcrystal material, the degree of the liquid crystal beingelectro-optically effected by the variations in temperature isrelatively decreased. Thus, the temperature dependency of the voltageoptical characteristics can be reduced.

As for the manufacturing method, it is preferable for the control ofdiameter and dispersion of liquid crystal particles that the mixture ofpolymer precursor and liquid crystal material is irradiated withultraviolet in the phase separation method, whereby the polymerprecursor is polymerized and phase-separated. The significance isspecifically described below.

In the 70^(th) to 77^(th) aspects, various kinds of liquid crystalmaterials, such as nematic liquid crystal, cholesteric liquid crystal,and smectic liquid crystal, which exhibit a liquid crystal state inaround room temperature, can be used as the liquid crystal. The liquidcrystal may be used singularly or in combination of two or more kinds.Also, the liquid crystal may be used with containing a two-tone coloringmatter therein. For example, polymer.liquid crystal complexes in whichtwo-tone coloring matters having different colors are contained may belaminated to form an optical element capable of full-color display.

The polymer compound used in the embodied forms has light permeabilityand holds the expression 4 in association with the liquid crystalforming the dispersion phase. The polymer.liquid crystal complexescapable to hold the expression 4 enable the liquid crystal molecules tobe oriented at small tilt angles to the wall of matrix, so that theresponse-to-electric-field of the liquid crystal display element and thetemperature dependency of the voltage optical characteristics isreduced. Preferably, the requirement of the expression 4 should bealways allowed to hold in a full temperature range (−10° C. to 60° C.)in actual operation of the liquid crystal display element. Thisformation can provide a good and stable display in a wide temperaturerange. The significance of the requirement of the expression 4-4 isdiscussed later.

γP>γLC  Expression 4-4

where γLC is surface tension of liquid crystal, and γP is criticalsurface tension of polymer compound.

Further, it is preferable that the polymer compound used has a goodaffinity for the liquid crystal; For example, the polymer compoundshaving a polar group such as a hydroxyl group, a carboxyl group or animino group should be preferably used. In addition, in consideration ofthe manufacturing circumstances, it is desirable that the polymercompound be produced by the polymer precursor being injected in betweenthe electrodes and thereafter polymerized. In this step, it ispreferable to use means for allowing polymerizable monomer andpolymerizable oligomer to be polymerized to produce the polymercompound, in terms of productivity of good quality of polymer.liquidcrystal complex.

Further, in the case of the polymer compound being produced by thepolymerization after injection, it is preferable that the polymerizablemonomer and polymerizable oligomer are both used and at least one of themonomer and the oligomer has the polar group, more preferably, the polargroup should include hydroxyl group, carboxyl group or imino group. Thisis because, when at least one of the monomer and the oligomer has thepolar group including the hydroxyl group, the polymer compound havinghigh hydrophilic nature (affinity) can be produced, and the polymercompound having high hydrophilic nature thus produced can provide betterwetting in the interface polymer/liquid crystal to improve the responseto electric field and the voltage optical characteristics of theelement. To be more specific, energetic stability in the interfacepolymer/liquid crystal is improved and the liquid crystal molecules canbe allowed to exist at smaller angles to a wall surface of the polymer.In addition, the better wetting reduces the tendency of transition oforientation pattern of the liquid crystal molecules (transition from thebipolar form to the radial form) due to variations in temperature, whichin turn can allow the temperature dependency of the liquid crystaldisplay element to be reduced.

The polymerizable polymer precursors which may be used include variouskinds of polymerizable materials which are polymerized by light(ultraviolet) and heat to produce a transparent polymer compound. Ingeneral, the monomer or oligomer having a polymerizable functional groupsuch as acrylate, methacrylate and epoxy is used. To be more specific,the polymerizable monomers which may be used include 2-ethylhexylacrylate, 2-hydroxyethyl acrylate, monohydroxyethyl acrylate phathalate,neopentyl glycol diacrylate and hexanedioldiacrylate. The oligomerswhich may be used include urethan acrylate, 1,6 hexanedioldiacrylate,pentaerythlytoldiacrylate monostearate, oligourethane acrylate,polyester acrylate and glycerine diglycidylether.

Examples of the polymerizable polymer precursors having the hydroxylgroup are M-5700 (monomer) and M233 (oligomer) available from TOAGOSEICO., LTD., and an example of the polymerizable polymer precursor havingthe carboxyl group is M-5400 (monomer) available from TOAGOSEI CO., LTD.Further, examples of the polymerizable polymer precursors having theimino group are M-1200 (oligomer) and M-1600 (oligomer) available fromTOAGOSEI CO., LTD. and UF-8001 available from KYOEISHA CO., LTD.

For meeting the requirement of the γP>γLC in a wide actual operatingtemperature range, the polymer material and the liquid crystal materialmust be combined properly. The polymer compound which is polymerized byuse of the polymerizable monomer and/or polymerizable oligomer havingthe hydroxyl group, carboxyl group and imino group, as described above,combined with the liquid crystal compatible therewith, e.g. MT5524available from CHISSO PETROCHEMICAL CORPORATION can realize the liquidcrystal display element capable of meeting the requirement of the γP>γLCin a wide actual operating temperature range.

The polymer.liquid crystal complex, which is a main component of thepolymer dispersion type liquid crystal display element according to theembodied forms, can be produced in any known manner, using theabove-listed materials. To be more specific, the known manners which maybe used includes a casting process in which a liquid crystal materialand a polymer material, after dissolved in a common solvent, are cast;an emulsion process in which the liquid crystal, after emulsified inaqueous solution of water-soluble polymer, is cast; and a phaseseparation process in which an uniform solution of liquid crystal andpolymer forming material is prepared and then is phase-separated bypolymerization.

Of the above-described processes, the phase separation process isdesirable for the liquid crystal polymer dispersion type liquid crystaldisplay element of the above described embodied forms. More preferableone is a photopolymerization phase separation process (usingultraviolet) using the molymerizable monomer and polymerizable oligomermentioned above. That is because, in the photopolymerization phaseseparation process, the liquid crystal is fully dispersed in advance inthe polymer precursor having a low viscosity and thereafter the polymerprecursor is polymerized to cause the phase separation, so that theparticle size of and the condition of dispersion of the liquid crystaldroplets can be easily controlled to produce a desirable polymer.liquidcrystal complex.

In the case of the photopolymerization phase separation process, apolymerization initiator should preferably be added to the polymerprecursor, for smooth polymerization of the polymerizable polymerprecursor. The polymerization initiators which may be used includecommercially available polymerization initiators, such as Darocure 1173,Darocure 4265 and Irgacure 184 available from CIBA-GEIGY LTD., inaddition to Benzyl Methyl Ketal. Two or more kinds of these may be usedin combination. The polymerization of the polymer precursor may beperformed in such a manner that the polymer precursor.liquid crystalmixture, which may include the polymerization initiator, is placed inbetween a pair of substrates and thereafter is irradiated withultraviolet from the top of the substrates. In this case, the intensityof ultraviolet to be irradiated should be 80 mW/cm² or more, preferably150 mW/cm² or more, and further preferably 200 mW/cm² or more. Theintensity of ultraviolet of 150 mW/cm² or more allows the opticalhysteresis to decrease when the operating temperature of the liquidcrystal display element becomes high temperatures, and the intensity ofultraviolet of 200 mW/cm² or more advantageously allows the orientationtransition temperature to decrease significantly.

On the other hand, it is also preferable that the intensity ofultraviolet may be reduced to 30 mW/cm² or less, to attempt to reducethe driving voltage of the liquid crystal display element. With theintensity of ultraviolet of 30 mW/cm² or less, the polymer compound isproduced so slowly that the particle size of the liquid crystal dropletscan be increased. With the liquid crystal droplets having large particlesize, the interfacial restrictive force of the polymer compound to theliquid crystal droplets is relatively reduced so that the elementcapable to be driven through an application of a reduced voltage can beobtained.

Further, the particle size of the liquid crystal droplets of the liquidcrystal display element should be set 0.8 μm to 2.5 μm, preferably, 1 μmto 2 μm, depending on what equipment is used and what is the intendeduse. That is because the liquid crystal droplets of 0.8 μm to 2.5 μmprovides the sufficient scattering effect, and the liquid crystaldroplets of 1 μm to 2 μm enables the liquid crystal panel to be driventhrough an application of a low voltage available for the TFT drive.

It is preferable that the cell gap for the polymer.liquid crystalcomplex to be filled in should be 5 μm or more, preferably 10 μm to 15μm. This set cell gap can allow both of improved light scatteringproperties and reduced driving voltage to be achieved by setting theparticle size of the liquid crystal droplets properly.

It is to be noted that the most characteristic feature of the polymerdispersion type liquid crystal display element of the above describedaspects of the invention is in that the γP>γLC holds, and no particularlimitation is given to any other factors than the factor of the γP>γLC.Thus, the liquid crystal display element of the invention can beproduced by any known producing methods plus the requirement of theγP>γLC. This enables the polymer dispersion type liquid crystal displayelement having the features of the embodied forms of the invention to beproduced with relative ease.

Incidentally, with the polymer dispersion type liquid crystal in whichmicroscopic liquid crystal droplets are dispersed in a matrix phase ofpolymer compound, contact areas of the liquid crystals with the polymercompound are significantly large, so that the orientation pattern of theliquid crystal molecules is greatly affected by the interfacialrestrictive force (physico-chemical force) of the polymer compound.Accordingly, the polymer dispersion type liquid crystal display elementis poorer in response to electric field, as compared with a conventionaltype liquid crystal display element which is regulated by the substratesonly. In addition, the intensity of the interfacial restrictive force issusceptible to temperature, so that, when operating temperature of theelement varies, the response to electric field (response time, inparticular) and voltage optical characteristics (transmission for anapplied voltage) of the liquid crystal molecules vary. Accordingly, thepolymer dispersion type liquid crystal display element has adisadvantage of lacking stability in display performance, as comparedwith conventional type elements such as the TN mode of liquid crystaldisplay element.

There is literature on the interfacial restrictive force of the polymercompound e.g. Sov. Phys. JETP 58(6), 1983, Liquid Crystal Dispersionswritten by P. S. Drzaic, World Scientific 1996, according to which thebipolar-form orientation having two poles is produced under hightemperatures of about room temperatures or more, as shown in FIG. 41(1),and the radial-form orientation of liquid crystals being orientedvertically to the interfaces is produced under low temperatures, asshown in FIG. 41(2).

FIG. 41(1) shows the state of liquid crystal molecules being orientedtoward two poles along a spherical surface, and FIG. 41(2) shows thestate of liquid crystal molecules being oriented with one ends thereoforienting toward the spherical surface and the other ends orientingtoward the center of the sphere.

The relationship between the interfacial restrictive force of thepolymer compound and the orientation of the liquid crystal molecules isconsidered below, based on the above literature. It is thought that theliquid crystal molecules in the liquid crystal droplets surrounded bythe polymer compound are strongly affected by the physico-chemical forcefrom the polymer compound of matrix and thereby are so oriented thatfree energy of the interface polymer/liquid crystal can be minimized. Asa result, the state of the liquid crystal molecules being oriented inparallel to the interfaces, i.e., the bipolar-form orientation shown inFIG. 41(1), is higher in energetic stability in the polymer/liquidcrystal interfacial boundary than the radial-form orientation of theliquid crystal molecules being oriented vertically to the interfaces asshown in FIG. 41(2). From this point, the liquid crystal molecules ofthe polymer/liquid crystal complex preferably take the bipolar-formorientation, rather than the radial-form orientation which is moresusceptible to temperature, while no voltage is applied.

On the other hand, it is desirable for obtaining a satisfactory contrastratio to allow the liquid crystal molecules to be oriented in parallelto the substrates when no voltage is applied and allow the same to beoriented vertically to the substrates quickly when a voltage larger thana threshold voltage is applied. In the radial-form orientation, however,a part of liquid crystal molecules are inevitably oriented vertically tothe substrates when no voltage is applied as well. Therefore, it is hardto obtain a satisfactory contrast ratio. In addition, since the liquidcrystal molecules are oriented with higher energy, it is difficult toallow them to be quickly oriented vertically to the substrates. Fromthis point also, the radial-form orientation is not desirable.

Hereupon, in the above described embodied forms, the element is formedby the polymer compound material and the liquid crystal being selectedso suitably that the γP>γLC can hold between the critical surfacetension γP of the polymer compound and the surface tension γLC of theliquid crystal. In this form of the element, the orientation pattern ofthe liquid crystal molecules during no voltage being applied takes thebipolar form and the liquid crystal molecules are oriented at small tiltangles to the wall surface of the polymer compound. This can provideimproved response to electric field and reduced temperature dependencyof the voltage optical characteristics.

Further, when the requirement of the γP>γLC is met by using polymercompound having polar group, such as hydroxyl group, carboxyl group orimino group, good wettability (affinity) between the liquid crystaldroplets and the polymer compound surrounding them is obtained, so thatthe liquid crystal molecules are allowed to stably exist in theinterface polymer/liquid crystal. This enables the tilt angles of theliquid crystal droplets to the wall surface of the polymer compound tobe further reduced, to make it hard to cause the orientation transitionbetween the bipolar form and the radial form. This can provide theresult of producing the liquid crystal display element having improvedresponse to electric field and reduced temperature dependency of thevoltage optical characteristics.

It is noted that the polymer dispersion type liquid crystal referred toin the fourth inventive group is not limited to the polymer.liquidcrystal complex only wherein droplets of the liquid crystal areinterspersed in an island form in the polymer compound, but may includenot only the one wherein the droplets of the liquid crystal arepartially associated in series with neighboring droplets but also theone (polymer network liquid crystal) wherein the droplets of the liquidcrystal are held in networks of the polymer compound of a threedimensional network. However, the formation for the droplets of theliquid crystal to be held in the networks of the polymer compound of thethree dimensional network form does not take the bipolar-formorientation pattern in general, because the interfacial restrictiveforce does not act on the droplets of the liquid crystal uniformly. Itis known however that even this formation allows the liquid crystalmolecules to be oriented vertically under low temperatures, to take theradial-like form orientation, so there may arise the above-describedproblem of strong temperature dependency in the response to electricfield. Accordingly, even in this case, the feature of γP>γLC of thepresent invention works effectively.

Finally, the principle of the liquid crystal display element of thefourth inventive group is illustrated in FIG. 40. Shown in this figureis the state of incident light 422 being turning transmitted light 424and scattered light 423 due to different molecular orientations in theliquid crystal droplets.

BRIEF DESCRIPTION OF THE DRAWINGS

First Inventive Group

FIG. 1 is a graph for illustrating the optical hysteresis, in the firstinventive group;

FIGS. 2(A) and (B) are diagrammatic illustrations of the rate ofpolymerization and the state of the liquid crystal droplets beingformed, in the first inventive group;

FIGS. 3(A) and (b) are diagrammatic illustrations of generating densityof the liquid crystal droplets and the state of the liquid crystaldroplets being formed, in the first inventive group;

FIG. 4 is a graph showing the capacitance measured in the relation withthe ultraviolet irradiation time, in the first inventive group;

FIG. 5 is a diagrammatic illustration of the relationship between thepolymerization temperature and the optical hysteresis and others, in thefirst inventive group;

FIG. 6 is a graph showing the relationship between the polymerizationtemperature and the optical hysteresis, in the first inventive group;

FIG. 7 is a graph showing the relationship between the polymerizationtemperature and the rate of polymerization, in the first inventivegroup;

FIG. 8 is a graph showing the relationship between the ultravioletintensity and the optical hysteresis, in the first inventive group;

FIG. 9 is a graph showing the relationship between the time T2 and theoptical hysteresis, in the first inventive group;

FIG. 10 is a sectional view of a liquid crystal display element of thefirst inventive group;

FIG. 11 is a view of an experimental apparatus of the first inventivegroup;

FIG. 12 is a graph showing the relationship between the ultravioletintensity and the polymerization temperature under which the opticalhysteresis is reduced to the minimum;

FIG. 13 is a graph showing the relationship between the time T1 and theoptical hysteresis, in the first inventive group;

FIG. 14 is a graph showing the relationship between the time T1 and thetime T2, in the first inventive group;

Second Inventive Group

FIG. 15 is a sectional view of a liquid crystal display element of thesecond inventive group;

FIG. 16 is an illustration of the state of liquid crystal droplets inthe liquid crystal display element of the second inventive group asobserved with a microscope;

FIG. 17 is an illustration of orientation patterns of a liquid crystalmolecule in the liquid crystal display element of the second inventivegroup;

FIG. 18 is a graph showing the applied voltage-transmittancecharacteristics of the liquid crystal display element of the secondinventive group;

FIG. 19 is a sectional view of the liquid crystal display element of thesecond inventive group;

FIG. 20 is a graph showing the relationship between the anchoring indexand the orientation temperature in the second inventive group;

FIG. 21 is a schematic view showing the structure of a productionapparatus of the liquid crystal display element of the second inventivegroup;

Third Inventive Group

FIG. 22 is a graph showing the voltage-capacitance characteristics andthe voltage-transmittance characteristics of the third inventive group;

FIG. 23 is a view showing the capacitance hysteresis and the opticalhysteresis of the third inventive group;

FIGS. 24 (A) and (b) are graphs showing the relationship between thecapacitance hysteresis and the optical hysteresis, in the thirdinventive group;

FIGS. 25 (A) and (b) are additional examples of the relationship betweenthe capacitance hysteresis and the optical hysteresis;

FIG. 26 is a sectional view of the structure of the liquid crystaldisplay element of the third inventive group;

FIG. 27 is a graph showing the relationship between the opticalhysteresis and the capacitance ratio %, in the third inventive group;

Fourth Inventive Group

FIG. 28 is a conceptually illustrating sectional view of a main part ofa liquid crystal display element of the fourth inventive group or ofconventional type;

FIG. 29 is a graph showing the relationship among the subtraction resultof γLC−γP, the value of γ, and the response time, in the fourthinventive group;

FIG. 30 is a graph showing the relationship between the value of γ, andthe response time, in the fourth inventive group;

FIG. 31 is a graph showing the relationship between the subtractionresult of γLC−γP and Δ V, in the fourth inventive group;

FIG. 32 is a schematic illustration of the structure in section ofanother embodiment of the polymer dispersion type liquid crystal displayelement of the fourth inventive group;

FIG. 33 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Example 2-1 of thefourth inventive group;

FIG. 34 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Example 2-2 of thefourth inventive group;

FIG. 35 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Example 2-3 of thefourth inventive group;

FIG. 36 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Example 2-4 of thefourth inventive group;

FIG. 37 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Example 2-5 of thefourth inventive group;

FIG. 38 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Example 2-6 of thefourth inventive group;

FIG. 39 is a graph showing the relationship between the temperature ofthe liquid crystal display element and the V90%, of Comparative Example1 comparative to Examples 2-1 to 2-6 of the fourth inventive group;

FIG. 40 is a schematically illustrating sectional view for illustratingthe principle of display of the liquid crystal display element using thepolymer dispersion type liquid crystal of the fourth inventive group;and

FIG. 41 is a schematic view showing the radial-form orientation and thebipolar-form orientation in the first inventive group.

BEST MODE FOR CARRYING OUT THE INVENTION

The detailed description of the above contents of the group of theinvention will be given in order below. The best mode of aspects of thepresent invention will become apparent from the description.

(1) Examples of First Inventive Group

Example 1-1

FIG. 10 is a sectional view of the liquid crystal display elementaccording to Example 1-1. In practice, an active matrix substrateforming thereon TFT transistors is used in this Example, though notshown here.

Polymer compound 112 and liquid crystal droplets 113 are placed withbeing dispersed in between glass substrates 110 having pixel electrodes111, and the liquid crystal droplets 113 are scattered in the polymercompound in the island form. The liquid crystal molecules 114 in theliquid crystal droplets 113 take a bipolar-form orientation pattern witha plurality of oriented poles on walls of the liquid crystal droplets113. The liquid crystal droplets 113 in the vicinity of the interfacesof the substrates are formed by their great circles contacting with thesubstrates.

The liquid crystal display element according to Example 1-1 thus formedis characterized by that all the liquid crystal droplets but those atthe interfaces of the substrates have substantially the same shape andsize, particularly in that variations in particle size of the liquidcrystal droplets are within 10%. The liquid crystal display element isproduced by the following method. In FIG. 10, some of the liquid crystaldroplets 113 have a partly jointed form, which may be of an individuallyseparated form. In addition, the polymer compound may be formed into anetwork form so that the liquid crystals can be held in between thenetworks.

Production of the Liquid Crystal Panel

(1) 89 wt % of polymerizable monomer (2-ethylhexyl acrylate), 9 wt % ofoligomer (Biscoart 828 available from OSAKA ORGANIC CHEMICAL INDUSTRY)and 1 wt % of polymerization initiator (Benzyl Methyl Ketal availablefrom NIPPON KAYAKU CO., LTD.) were mixed, and then 1 wt % of HDDA(KAYARAD HDDA available from NIPPON KAYAKU CO., LTD.) was added to themixture, for the purpose of controlling the interfacial restrictiveforce. 80 wt % of liquid crystal of TL205 (available from Merck JapanLimited) was added to 20 wt % of the thus obtained polymer precursormixture to form liquid crystal polymer precursor compatible solution.

The thermal phase separation temperature of the above liquid crystalpolymer precursor compatible solution was measured with a Mettler, themeasurement result being 10° C.

(2) A pixel electrode 111, a source line, a gate line and others wereprovided for a glass substrate 110 and the counter substrate 116 havinga counter electrode 117 through the techniques of vacuum deposition andetching to thereby produce an active matrix substrate. Further, aninsulating film material was printed on the substrate by a printingmethod and then was cured in an oven, to form insulating film 115thereon. OPTOMER AL8534 (available from JAPAN Synthetic Rubber Co.,Ltd.) was used as the above insulating film material. Also, a glassplate 1737 available from CORNING INC. (1.1 mm in thickness) was used asthe glass substrate.

(3) After a similar insulating film 115 was formed on the countersubstrate 116 having the counter electrode 117, the glass substrate 110and the counter substrate 116 were laminated to each other through glassspacers at an interval of 13 μm.

(4) The liquid crystal polymer precursor compatible solution wasinjected in between the laminated substrates (hereinafter it is simplyreferred to as “the panel”) via a vacuum injection method, to produce aliquid crystal panel 120 (a before-phase-separation one). Apolymerization monitoring liquid crystal panel 121 (See FIG. 11)described later was produced in an analogous manner. However, thepolymerization monitoring liquid crystal panel 121 was not so formed asto have TFT, though transference electrodes were formed on both of theupper and lower substrates.

Phase Separation Process

The phase separation process is described with reference to FIG. 11.First, a liquid bath 125 made of silica glass was located at the upperside of the liquid crystal panels 120, 121 formed as described above, inorder to control the surface temperature of the liquid crystal panels.The liquid bath 125 is connected to a circulating high temperature tank123 so that water of regulated temperature can be circulatedtherethrough. Further, on the liquid bath 125 was disposed anultraviolet filter 126 (Color glass filter UV35 available from TOSHIBAGLASS CO., LTD.) capable to filter out light wavelength of 350 nm at itspeak to 50% in intensity. Next, a capacity measuring apparatus 127 (LFIMPEDANCE ANALYZER 4192A available from Hewlett-Packard) was connectedto the electrodes of the polymerization-monitoring liquid crystal panel121.

Thereafter, the panel was set at 19° C. in surface temperature byadjusting the temperature of the circulating water and then wasirradiated with ultraviolet at the intensity of 200 mW/cm² for about 30seconds by use of an ultraviolet irradiating apparatus 128 having anextra-high pressure mercury vapor lamp as a light source(UVA702-IMNSC-BB01 available from USHIO INC.), whereby the polymerizablemonomer was polymerized to produce the polymer dispersion type liquidcrystal element. The intensity of ultraviolet was measured at a point onthe surface of the panel via an illuminance meter (ultravioletIlluminance meter UV-M02 available from ORC MANUFACTURING CO., LTD.).

Evaluation of Phase Separation Condition

1) Time T1, T2

The variations in the capacitance of the liquid crystal panel 121 weremeasured in relation to the time after the initiation of irradiation ofultraviolet to determine T₁₀₋₉₀ which is associated with the time T1,T2. It is noted here that the T₁₀₋₉₀ is intended to mean the timerequired for an advance ratio of phase separation to reach 90% from 10%,when the advance ratio of the phase separation at which all the liquidcrystals are separated from the liquid crystal polymer precursorcompatible solution is set 100%.

The capacitance was measured with the capacitance measuring apparatus127 under the conditions of 600 Hz in measuring frequency; 0.5V inmeasuring voltage and +10V in bias voltage. The measurement result isshown in FIG. 4. The time T1 measured on the basis of FIG. 4 was 2.2seconds and the time T₁₀₋₉₀ was 2.9 seconds.

2) Properties of Liquid Crystal Droplets

The properties of the liquid crystal droplets were estimated by thefollowing techniques.

Two glass substrates, identical to the above ones, except no TFTelements being formed, were used to produce the polymer dispersion typeliquid crystal panel in an analogous manner. After the substrates werepeeled off from the liquid crystal panel and the liquid crystal dropletswere washed out, the resultant polymer matrix was observed with amicroscope and also was measured on the average particle size by use ofan image processing apparatus. The result was the average particle sizeof 1.2 μm. Also, the variation in particle size was 5%. Thus, it wasconfirmed that the produced liquid crystal droplets had substantiallythe same shape and size. It is noted that the terminology of “variationsin particle size” used herein are intended to mean “standard deviationin average particle size”.

It is thought that the above results have no great effect on theproperties of the liquid crystal droplets due to the presence or absenceof the TFT elements, so the results are thought to reflect theproperties of the liquid crystal droplets in the liquid crystal displayelement of Example 1-1.

It was observed in the microscopic observation that there were someliquid crystal droplets distorted or some neighboring liquid crystaldroplets partly jointed to each other. That is thought to be because theproportion of the liquid crystals in Example 1-1 is as high as 80%.

3) Electro-optical Characteristics

The electro-optical characteristics of the liquid crystal displayelement were measured in the following steps.

The driving circuit was connected to the liquid crystal panelseparately, to drive the TFT. A voltage varying continuously from 0 V atthe minimum to 15 V at the maximum was applied across the counterelectrode and pixel electrode of the liquid crystal panel, to reversethe direction of voltage sweep, for measurement of the opticalhysteresis. The panel transmittance at measurement was measured by useof a liquid crystal evaluating apparatus (LCD5000 available from OTSUKAELECTRONICS CO., LTD.).

When the optical hysteresis is defined by a percentage of a valueobtained by the difference between the intensity of transmitted light atthe time of raised voltage and that at the time of dropped voltageduring the application of the same voltage being divided by theintensity of transmitted light at the time of application of 15 V, theoptical hysteresis (maximum value) was 1%. Also, a good display ofalmost no residual image resulting from the optical hysteresis wasobtained over the full levels of gray scale, even when the gray scalewas displayed to flash on and off.

Further, it was additionally confirmed that if variations in the liquidcrystal droplets was not more than 10%, the optical hysteresis came to2% or less and good display was obtained.

The polymerization monitoring liquid crystal panel, used in the aboveexample in order to monitor the degree of polymerization of the liquidcrystal panel, serves as a guide for determination of the polymerizationconditions for an additional liquid crystal polymer precursor compatiblesolution. Accordingly, this element is not always indispensable. Inaddition, the intensity of ultraviolet and the polymerizationtemperature may be used as a parameter for determination of thepolymerization conditions, but the degree of polymerization monitoredfor the determination can provide more effects on reduction ofunevenness in mass production.

The intensity of ultraviolet should preferably be 160 mW/cm² forallowance in practical performances. That intensity can provide theelement having the optical hysteresis of 1% or less with good yields.

Further, the intensity of ultraviolet may be varied by varying theintensity itself of an ultraviolet irradiation lamp or by reducing theintensity of ultraviolet of particular wavelengths by use of a filter.In the case of varying the intensity of the lamp, an extra-high pressuremercury vapor lamp, a high pressure mercury vapor lamp and a metalhalide lamp, for example, may be used. The extra-high pressure mercuryvapor lamp and the high pressure mercury vapor lamp, peaking at thewavelength of ultraviolet of 365 nm and thus being low in intensity of avisible region, have the advantage of providing reduced deposition ofliquid crystals and thus presenting high reliability. On the other hand,the metal halide lamp, in which a lamp intensity exists in the visibleregion, has a problem of inferior reliability.

In addition, the filter, when used, has desirably the capability ofreducing the wavelength of 350 nm or less at its peak to about 50% inintensity, as mentioned above, to allow for an absorbing wavelengthwhich can cause the deposition of liquid crystals and the polymer and arequired intensity of ultraviolet for the phase separation.

Also, as long as the required intensity of ultraviolet for the phaseseparation can be obtained, ultraviolet of a longer wavelength regionshould preferably be used by filtering out ultraviolet of a shorterwavelength region. This is because the liquid crystals tend to bedecomposed by ultraviolet of shorter wavelength regions rather than byultraviolet of longer wavelength regions. The inventors confirmed thateven when the filter capable of reducing wavelengths of shorterwavelength regions of 360 nm or of 370 nm or less was used,polymerization could be allowed to smoothly progress by increasing theintensity of ultraviolet.

Example 1-2

The liquid crystal display element of Example 1-2 was produced in asimilar manner to that in Example 1-1, except that the temperature ofthe liquid crystal panel (polymerization temperature) and the intensityof ultraviolet at the time of irradiation of ultraviolet were changed.In addition, the evaluation was made by use of the same apparatus and inthe same manner as in Example 1-1.

The temperature of the liquid crystal panel was set at any selectedtemperature while being measured by use of a thermocouple. In addition,the degree of polymerization of the polymer was changed by allowing theliquid crystal panel to be irradiated with ultraviolet at any selectedintensity and for any selected time by use of an ultraviolet irradiatingapparatus 128. The degree of polymerization was measured with thecapacitance monitored by a capacitance measuring apparatus 127.

Shown in FIG. 6 is the relationship between the polymerizationtemperature and the optical hysteresis. It was confirmed from FIG. 6that the element of minimized optical hysteresis was produced bychanging the polymerization temperature. Shown in FIG. 12 is therelationship between the polymerization temperature exhibiting theminimum value and the intensity of ultraviolet, from which it wasconfirmed that the liquid crystal display element of reduced opticalhysteresis could be produced by regulating the polymerizationtemperature suitably in association with the intensity of ultraviolet.

In other words, it was demonstrated from Example 1-2 that even when thesame liquid crystal polymer precursor compatible solution was used, thepolymer dispersion type liquid crystal display element of reducedoptical hysteresis can be accomplished by regulating the polymerizationtemperature and the intensity of ultraviolet adequately.

Example 1-3

The liquid crystal display element of Example 1-3 was produced in asimilar manner to that in Example 1-1, except that the polymerizationtemperature was changed within the range from a thermal phase separationtemperature of the liquid crystal polymer precursor compatible solutionto a temperature deviating therefrom as high as +20° C. and also theintensity of ultraviolet was changed within the range from 100 mW/cm² to550 mW/cm². In addition, the evaluation was made by use of the sameapparatus and in the same manner as in Example 1-1.

In Example 1-3, the rate of polymerization, the degree of polymerization(viscosity, hardness) of polymer around separated liquid crystal nucleiand the generating density of the separated nuclei as described abovewere controlled by controlling the time T1 from the initiation ofirradiation of ultraviolet to the initiation of phase separation of theliquid crystal polymer precursor compatible solution and the time T₁₀₋₉₀from the initiation of separation of the liquid crystal (separatednuclei) to the completion of phase separation.

Shown in FIG. 13 is the relationship between the time T1 and the opticalhysteresis of the element of Example 1-3, and shown in FIG. 9 is therelationship between the time T2 (or rather T₁₀₋₉₀) and the opticalhysteresis.

As clearly seen from FIG. 9, the time T2 and the optical hysteresisshowed a substantially positive correlation therebetween, irrespectiveof the polymerization temperature and the intensity of ultraviolet. Thisclarified that the optical hysteresis could be reduced by controllingthe time T2.

On the other hand, it was seen from FIG. 13 that the time T1 was notcorrelated with the optical hysteresis so much as the time T₁₀₋₉₀ was.However, it was confirmed that at the intensity of ultraviolet of 200mW/cm² or less, there was a positive correlation between the time T1 andthe optical hysteresis, while also, at the intensity of ultraviolet of300 mW/cm² or more, a substantially constant optical hysteresispresented, irrespective of the time T1. It was proven from this that atthe intensity of ultraviolet of 200 mW/cm² or less, the opticalhysteresis could be reduced by controlling the time T1.

Also, it was proven from FIGS. 9 and 13 that the optical hysteresis of2% or less requires the time T1 and the time T₁₀₋₉₀ to be reduced to 5seconds or less and 6 seconds or less, respectively, and that theoptical hysteresis of 1.5% or less requires the time T1 and the timeT₁₀₋₉₀ to be reduced to 4 seconds or less and 5 seconds or less,respectively. Further, it was proven that the optical hysteresis of 1%or less requires the time T₁₀₋₉₀ reduced to 3 seconds or less and thatthe optical hysteresis of 0.5% or less requires the time T₁₀₋₉₀ toreduced to 1.5 seconds or less.

Shown in FIG. 14 is the relationship between the time T1 and the timeT₁₀₋₉₀ presented with reference to the intensity of ultraviolet. Asclarified from FIG. 14, the time T1 and the time T₁₀₋₉₀ were found to becorrelated to each other so close that they could be approximated withT₁₀₋₉₀ 32 a·T1+b (linear function). Also, it was proven that the numbera in the linear function ranged from 0.4 or more to 0.6 or less withinthe range of 100 mW/cm² to 550 mW/cm² in intensity of ultraviolet.Accordingly, using the linear function equation, the values of the timeT1 and the time T₁₀₋₉₀ can be estimated to enable the polymerization tobe controlled further efficiently.

A method of forming the element having a small optical hysteresis bymaking the use of the above FIGS. 7, 9 and 14 will be described here.

The time T₁₀₋₉₀ for enabling a desired optical hysteresis is read outfrom FIG. 9. Then, the time T1 related to the time T₁₀₋₉₀ is read outwith reference to the intensity of ultraviolet from FIG. 14. Theresulting time T1 is fitted to the ordinance in FIG. 7 and thepolymerization temperature is read out from a line of the time T1 (♦-♦).Thus, the intensity of ultraviolet and the polymerization temperaturerequired for the element of a desired optical hysteresis to be producedcan be determined. Using these requirements, the element structurehaving reduced optical hysteresis characteristics (the structure ofpolymer dispersion type liquid crystal, or directly, the formation andstructure of liquid crystal droplets related with the polymer matrix)can be realized. More specific description on this will be given below,taking the case of the optical hysteresis being brought to 1% as anexample. In this example, the thermal phase separation temperature ofthe liquid crystal polymer precursor compatible solution is assumed tobe 10° C.

First, the time T₁₀₋₉₀ for enabling the optical hysteresis of 1% readout from FIG. 9 is 3 seconds. From FIG. 14, the T1 corresponding to the3 seconds (T₁₀₋₉₀) can be read as about 2 seconds for the intensity ofultraviolet of 200 mW/cm², about 3.6 seconds for the intensity ofultraviolet of 300 mW/cm², and about 4.4 seconds for the intensity ofultraviolet of 400 mW/cm². When the polymerization time corresponding tothe obtained time T1 is read out in FIG. 7, the result being of 2sec.→19° C., 3.6 sec.→32° C., and 4.4 sec.→44° C. The results are listedin TABLE 1. It is understood from this that the polymer dispersion typeliquid crystal display element having the optical hysteresis of 1% couldbe realized: by irradiating the ultraviolet of 200 mW/cm² in intensityfor about 30 seconds, with the polymerization temperature (liquidcrystal panel temperature) set at 19° C. (thermal phase separationtemperature +9° C.); by irradiating the ultraviolet of 300 mW/cm² inintensity for about 30 seconds, with the polymerization temperature setat 32° C. (thermal phase separation temperature +22° C.); or byirradiating the ultraviolet of 400 mW/cm² in intensity for about 15seconds, with the polymerization temperature set at 44° C. (thermalphase separation temperature +34° C.).

TABLE 1-1 Deviation from Thermal Phase Intensity of PolymerizationSeparation Ultraviolet Time T1 Time T₁₀₋₉₀ Temperature Temperature(mW/cm²) (Second) (Second) (° C.) (° C.) 200 2.0 3.0 19 +9 300 3.6 3.032 +22 400 4.4 3.0 44 +34

Attention should be paid to the following for selection of theabove-listed conditions. When the polymerization temperature is as highas 17° C. or more in deviation from the thermal phase separationtemperature, the liquid crystal droplets have the tendency to bedistorted due to scratch defects of the substrates or something. Due tothis, it is preferable to avoid selecting a temperature higher than athermal phase separation temperature by 17° C. or more as thepolymerization temperature. Take the above case for instance, theconditions of the intensity of ultraviolet of 200 mW/cm² and thepolymerization temperature of 19° C. should preferably be selected, forexample.

Example 1-4

The liquid crystal display element of Example 1-4 was produced in asimilar manner to that in Example 1-1, except that the polymerizationtemperature was kept constant at 13° C. and also the intensity ofultraviolet was changed within the range from 20 mW/cm² to 550 mW/cm².In addition, the evaluation was made by use of the same apparatus and inthe same manner as in Example 1-1.

The measuring results of the optical hysteresis are shown in FIG. 8. Asshown in FIG. 8, with increasing intensity of ultraviolet, the opticalhysteresis was reduced significantly. At the intensity of 100 mW/cm²,the optical hysteresis came to 1.5%. Also, at the intensity of 200mW/cm², the optical hysteresis came to 1%, and at the intensity of 300mW/cm² and 500 mW/cm², the optical hysteresis came to 0.8% and 0.5%,respectively.

When 126 levels of gray scale were displayed to flash on and off byusing the liquid crystal display element of the optical hysteresis of1%, it was confirmed that residual images and things like that could bewell reduced to produce a good display enough for applications to OAincluding data projections.

With the optical hysteresis of 0.5%, a good gray scale display wasobtained even at the 256 levels of gray scale display, thus achieving agood image for a full color moving picture as well.

It is then clearly seen from Examples 1-1 and 1-2 that the change of theintensity of ultraviolet is a consequence of the control of theabove-described time T1 and T₁₀₋₉₀.

In addition, there was provided the effect that with increasingintensity of ultraviolet, unevenness of polymerization, resulting from ascratch defect on the substrates or unevenness of irradiation,decreased. This is because, with increasing intensity of ultraviolet,the rate of polymerization increases so that the liquid crystal dropletscan be prevented from growing unevenly along the scratch defects.

Example 1-5

Example 1-5 is distinguishable in that the temperature of element of theliquid crystal display element at the time of irradiation of ultravioletis in the range of from 1° C. or more to 15° C. or less in deviationfrom a thermal phase separation temperature of the mixed solution andthat the time T1 and the time T₁₀₋₉₀ are controlled by changing asurface temperature of the element. The remaining requirements are thesame as those in Example 1-1.

The polymerization temperature was set within the range of from not lessthan a thermal phase separation temperature of the liquid crystal andpolymer to not more than a temperature deviating therefrom as high as+20° C. Also, the intensity of ultraviolet was set in the range of notmore than 110 mW/cm², 200 mW/cm², 300 mW/cm², 400 mW/cm², and 550mW/cm².

Measurements of the optical hysteresis (a maximum value) under thetemperature of element of 30° C. are shown in FIG. 6.

When polymerization temperatures were changed with reference to therespective intensity of ultraviolet, the magnitude of any of the opticalhysteresis varied, each presenting the polymerization temperature atwhich the optical hysteresis exhibited a minimum value. Also, withincreasing intensity of ultraviolet, the polymerization temperaturesexhibiting the minimum values were shifted toward higher temperatures.Further, with the intensity of ultraviolet of not less than 200 mW/cm²,downward depressed curves were plotted, each showing the existence ofthe polymerization temperature providing the minimum optical hysteresis(the minimum value). The polymerization temperatures at which theoptical hysteresis come to minimum range from about 12° C. to about 23°C., which are higher than the thermal phase separation temperature (10°C.) by 2-13° C.

It was proven from FIGS. 6 and 12 that the element of small opticalhysteresis could be produced by proper combination of the intensity ofultraviolet and the polymerization temperature. It is clearly seen fromExamples 1-2 and 1-3 that the change of polymerization temperature is aconsequence of the control of the above-described time T1 and T₁₀₋₉₀.

Example 1-6

In this example, the polymerization temperature under which the opticalhysteresis comes to an almost minimum value was selected. To be morespecific, with the intensity of ultraviolet set at 200 mW/cm²(irradiated for 30 seconds) and the polymerization temperature set at atemperature (17° C.) higher than the thermal phase separationtemperature (10° C.) by 7° C., a liquid crystal display element wasproduced. The remaining requirements are the same as those of Example1-1.

The element thus produced had the maximum optical hysteresis of 0.8%under the temperature of element of 30° C.

Further, with the intensity of ultraviolet set at 300 mW/cm² and thepolymerization temperature set at a temperature (19° C.) higher than thethermal phase separation temperature by 9° C., a liquid crystal displayelement was produced in an analogous manner.

The element thus produced had the optical hysteresis of 0.6% under thetemperature of element of 30° C. and was confirmed to provide a goodimage at the 256 levels of gray scale display.

Further, it was confirmed that with increasing intensity of ultraviolet,the rate of polymerization increased to allow the liquid crystaldroplets to be uniform, but, with the intensity of ultraviolet exceeding400 mW/cm², the optical hysteresis increased by the order of 20% in useunder a low temperature (not more than 5° C.). Due to this, in order tosuppress deterioration of the optical hysteresis under low temperatures,the intensity of ultraviolet should be set to be not more than 400mW/cm² and also the polymerization temperature should be lower than thethermal phase separation temperature by 5 to 13° C. It should be notedthat when the intensity of ultraviolet is strong, there is a possiblefear that the liquid crystals may be decomposed and excessively reducedin size to lower the scattering characteristics.

Example 1-7

As a substitute for the composition of the polymer precursor mixturedescribed in Example 1-1, a polymer precursor mixture was produced, with2-ethylhexyl acrylate (polymerizable monomer) mixed to the mixture inproportion of 88 wt %, HDDA (KARARAD) mixed in the proportion of 2 wt %,and the oligomer and the polymerization initiator mixed in the sameproportions as those in Example 1-1. Then, the resulting polymerprecursor mixture and the above-described liquid crystal material TL205were mixed each other in the proportions of 20 wt % and 80 wt %,respectively, to produce a liquid crystal polymer precursor compatiblesolution. The compatible solution thus produced was injected in thepanel. Thereafter, with the panel temperature (polymerizationtemperature) set at a temperature higher than the thermal phaseseparation temperature by 10° C., the panel was irradiated withultraviolet with the intensity of 300 mW/cm² for 30 seconds topolymerize the polymer precursor, to thereby produce the polymerdispersion type liquid crystal display element.

The element thus produced was measured in respect of the opticalhysteresis, with the temperature of element (operating temperature)varied in the range of 0° C. to 70° C. The measurement was made with thesame apparatus and in the same manner as those in Example 1-1. With theelement driven via TFT, its gray scale display properties were observed,the results being shown in TABLE 1-2.

As to the marks used in TABLE 1-2, {circle around (∘)} represents a verygood gray scale display; ◯ represents a good gray scale display; and Δrepresents a slightly inferior gray scale display.

TABLE 1-2 Evaluation of Display Temperature ° C. Optical hysteresis %Performance 0 2.5 Δ 5 1.3 ◯ 10 1.0 ⊚ 30 0.8 ⊚ 50 1.0 ⊚ 70 0.9 ⊚

As clearly seen from TABLE 1-2, the liquid crystal display elementexhibited a good display performance in the operating temperatureranging from 5° C. to 70° C. It was proven from the experimental resultsthat the liquid crystal display element capable of delivering a gooddisplay performance could be produced even in temperatures of not morethan room temperatures by adding an additive capable to allow theinterfacial restrictive force (anchoring), like HDDA, and controllingthe polymerization temperature and intensity of ultraviolet in the phaseseparation operation properly.

The additive capable to adjust the interfacial restrictive force is notlimited to the HDDA disclosed above, but various kinds of monofunctionalmonomers and/or multifunctional monomers may be used as the additive. Ofthose additives, bifunctional monomer is particularly preferable in thatthe effect of improving the optical hysteresis under low temperatures isenhanced. The monofunctional monomers which may be used include, forexample, isostearyl acrylate (Light Acrylate IS-A available fromKYOEISHA CO., LTD.). The bifunctional monomers which may be usedinclude, for example, triethylene glycol diacrylate (3EG-A), PEG #200diacrylate (4EG-A), PEG #400 diacrylate (9EG-A), neopentyl glycoldiacrylate (NP-A), 1,6-hexandiol diacrylate (1.6 HX-A; all of the aboveavailable from KYOEISHA CHEMICAL CO., LTD.). These may be used singly orin combination of two or more kinds.

Other matters

The insulating films which may be used in the first inventive group arenot necessarily limited to those described in the above Examples, butmay include either of those of polyimide type and those of polyamic acidtype. Again, the insulating films may be substituted for inorganicinsulating films (SiO₂ and others). The insulating film, when used,provides the effect of enhancing the retention of voltage. Additionally,the insulating film of high surface energy (surface tension) in theinterface with the liquid crystals, when used, provides acceleratedseparation speed of the liquid crystals, to lead to reduction of opticalhysteresis.

Also, combination of the liquid crystal precursor compatible solution isnot limited to those disclosed in the above Examples, either, but anycombination will do, as long as the liquid crystal and the polymerprecursor are allowed to be compatible and also are allowed to be phaseseparated by irradiation of ultraviolet to be copolymerized. Forexample, PNM201 (available from DAINIPPON INK AND CHEMICALS, INC.) maybe used as the liquid crystal polymer precursor compatible solution.When PNM201 is used, both of the polymer dispersion type liquid crystalin the narrow sense in which liquid crystal droplets are held incontinuous polymer matrix phase and the polymer network type liquidcrystal can be allowed to be prepared by changing the preparationconditions.

Further, in general, the thermal phase separation temperature varieswith variations in composition of the liquid crystal polymer precursorcompatible solution. Due to this, an absolute value of thepolymerization temperature must be varied in response to the thermalphase separation temperature of the liquid crystal polymer precursorcompatible solution. It was confirmed by the inventors that byequalizing the relative temperature differences between thepolymerization temperature and the thermal phase separation temperature,substantially the same effect could be produced even with thecomposition of the compatible solution varied. For example, PNM201 hasthe phase separation temperature of 17° C., so the polymerizationtemperature is determined with reference to this given temperature.Specifically, the polymerization temperature should preferably be in therange of about 20° C. to about 32° C.

The panel gap is not limited to those disclosed in Examples above, butis simply required to be not less than 5 μm. By letting the panel gap bein the range of from not less than 10 μm to not more than 15 μm, inparticular, the driving voltage and the scattering power can be allowedto be compatible.

The particle size of the liquid crystal droplets in the range of fromnot less than 0.8 μm to not more than 2.5 μm can provide the elementhaving an excellent scattering power. In particular, by letting theparticle size of the liquid crystal droplets be in the range of from notless than 1 μm to not more than 2 μm and setting the panel gapadequately, the element capable of being driven by a low voltage can beattained.

Means for controlling the panel temperature may adopt any form as longas it can keep the panel temperature constant and be capable ofirradiation of ultraviolet. For example, a Peltier element may be used.Alternatively, a temperature control of only one side of the liquidcrystal panel may be adopted.

Also, not less than 10 seconds is enough for the irradiation time ofultraviolet.

The technique of monitoring the degree of polymerization (the degree ofprogress of polymerization) with a suitable apparatus like the onedescribed in the above Examples provides the effect that the irradiationtime can be determined, with the degree of polymerization beingobserved. The above-said apparatus may alternatively be substituted forany other suitable means monitor the intensity of transmitted light andreflected light, to determine the degree of polymerization. Further, themeans for monitoring the degree of polymerization and the ultravioletirradiating apparatus can be associated with each other in their on-offmode, to allow the irradiation to stop automatically.

The liquid crystal polymer compatible solution may take differentproportions of the liquid crystal to the liquid crystal polymercompatible solution other than 80 wt %, but the proportion of the liquidcrystal should preferably be in the range of 70 wt % to 90 wt % in termsof the scattering characteristics. With increasing proportion of liquidcrystal, the liquid crystal droplets tend to be distorted, to lead toincrease in optical hysteresis. Thus, in the case of increasedproportion of liquid crystal, the operation and effect of the presentinvention of controllably restricting the intensity of ultraviolet andpolymerization temperature properly is exhibited further significantly.

(2) Examples of Second Inventive Group

Example 2-1

The liquid crystal display element according to Example 2-1 ischaracterized in that the bipolar-form orientation pattern is maintainedin the temperature range for the liquid crystal display element to beused. For this purpose, the transition temperature for the orientationpattern to be transformed from the bipolar-form orientation pattern tothe radial-form orientation pattern is attempted to be reduced bydecreasing tilt angles of the liquid crystal molecules at theirinterfaces with polymer.

FIG. 15 is a sectional view of a liquid crystal display elementaccording to Example 2-1. In practice, an active matrix substrateforming thereon TFT (Thin Film Transistor) is used in this Example,though not shown here.

As shown in the same figure, a liquid crystal layer comprising polymercompound 202 and liquid crystal droplets 203 is arranged between anactive matrix substrate 208 and a counter substrate 206 which aredisposed facing each other. The active matrix substrate 208 includes aglass substrate 200 on which a pixel electrode 201 and an insulatingfilm 205 are formed. On the other hand, the counter substrate 206includes a glass substrate 200 on which a counter electrode 207 and aninsulating film 205 are formed. The liquid crystal droplets 203 in theliquid crystal layer are dispersed and scattered in the island form inthe polymer compound 202. The liquid crystal droplets 203 take thebipolar-form orientation pattern in which the liquid crystal molecules204 each have variously oriented poles in the vicinity of theirinterface with the polymer compound 202. Though the liquid crystaldroplets 203 shown in FIG. 15 are individually separated from eachother, some neighboring liquid crystal droplets may partially contactwith each other to be associated in series. In addition, the formationin which polymer compound 202 are formed in the network form and theliquid crystals are held in between the networks of the polymer compoundmay be adopted.

The above-described liquid crystal display element was produced in thefollowing manner.

(1) Following materials, i.e.,

(a) 89% of polymerizable monomer (2 ethylhexyl acrylate);

(b) 9% of oligomer (Biscourt 828 available from OSAKA ORGANIC CHEMICALINDUSTRY);

(c) 1% of polymerization initiator (Benzyl Methyl Ketal available fromNIPPON KAYAKU CO., LTD.) were mixed, and then

(d) 1% of 1,6-hexandiol diacrylate of KS-HDDA (KAYARAD HDDA availablefrom NIPPON KAYAKU CO., LTD.) for controlling the interfacialrestrictive force was added to the mixture, to prepare a mixed solution.

Then, 80% of liquid crystal material TL205 (available from Merck JapanLimited) was added to 20% of the thus prepared mixed solution, toprepare liquid crystal polymer precursor compatible solution.

(2) A pixel electrode 201, a source line, a gate line, TFT elements andothers were formed on the glass substrate 200 through the techniques ofvacuum deposition and etching. Further, an alignment layer material ofOPTOMER AL8534 (available from JAPAN Synthetic Rubber Co., Ltd.) wasapplied on the pixel electrode 201 by a printing method and then wascured in an oven, to form an insulating film 205 thereon, thus producingan active matrix substrate 208.

(3) As in the case of the above (2), the counter electrode 207 and theinsulating film 205 were formed on the glass substrate 200, to producethe counter substrate 206.

(4) The active matrix substrate 208 and the counter substrate 206 werelaminated to each other through glass spacers, not shown, at an intervalof 13 μm.

(5) The liquid crystal polymer precursor compatible solution describedin the above (1) was injected in a space between the active matrixsubstrate 208 and the counter substrate 206 via a vacuum injectionmethod, to produce a liquid crystal panel.

(6) With the temperature of the liquid crystal panel kept at 13° C. (3°C. higher than the thermal phase separation temperature), the liquidcrystal panel was irradiated with ultraviolet of the intensity of 160mW/cm² to polymerize the polymerizable monomers in the liquid crystalpolymer precursor compatible solution, to thereby produce the polymerdispersion type liquid crystal display element. The intensity ofultraviolet above was confirmed by measuring with an illuminance meter.

It is difficult to make direct measurements of the tilt angles of theliquid crystal molecules 204 at the interface of the liquid crystaldroplets 203 of the thus produced liquid crystal display element withthe polymer compound 202, but it is possible to determine the tiltangles by the following manner. The mixed solution, which comprises thepolymerizable monomer, the oligomer, the polymerization initiator andthe interfacial restrictive force controlling agent as described in theabove (1), was applied on the glass substrate, which was then coveredwith another glass substrate. The resulting liquid crystal panel wasirradiated with ultraviolet under the same condition as in the above(6), to be cured into a thin layer form. Then, the liquid crystalmaterial described in the above (1) was dripped on the thin layer andcontact angles of the liquid crystal material dripped were measured todetermine the tilt angles, the measurement results being 5°.

Also, it is possible to determine the particle size of the liquidcrystal droplets 203 by the following manner. First, a pseudo-liquidcrystal display element was produced with the same composition and underthe same conditions as in the above-described liquid crystal displayelement, but with only difference in that the above-described countersubstrate 206 and active matrix substrate 208 were substituted for apair of single glass substrates. Then, the glass substrates were peeledoff from the element, and the liquid crystal droplets were washed out.The remaining part in which the liquid crystal droplets had existed wasobserved under the microscope, to determine a mean value of the particlesize by use of an image processor, the result being 1.2 μm.

From this, the liquid crystal display element using the substratesforming thereon the above-described TFT elements is presumed to alsohave the same alone particle size of 1.2 μm. It is noted that due to theproportion of the liquid crystals of the liquid crystal display elementof this Example being as high as 80%, the liquid crystal droplets 203are not necessarily spherical in shape completely separated from eachother, but some are of somewhat distorted spherical by some neighboringliquid crystal droplets 203 being partially jointed together to form acontinuum structure.

Next, the orientation patterns of the liquid crystals responsive toambient temperatures were observed. When there exist a plurality ofliquid crystal droplets 203 orienting in the vertical direction to theglass substrate 200, transmitted light is scattered to make itimpossible to make the direct measurements in this observation. However,it is possible to make the confirmations by the following manner.Specifically, adequate models of liquid crystal droplets 203′, eachhaving a size enough to be observed under the microscope, are formedfrom the same composition, and the experiments are made for the models,for the observation purpose. To be more specific, with the panel gap setat 10 μm, the liquid crystal droplets 203′ having the diameter of 12 μmare formed and observed. In this case, the liquid crystal droplets 203′formed take the formation of their being somewhat compressed in adirection vertical to substrates 206′.208′, as shown in FIG. 3.

When the observation of the liquid crystal droplets 203′ was made underambient temperature of 30° C. with a polarization microscope having apolarizing plate disposed on a cross nicole, the liquid crystal droplets203′ shown in FIG. 16(a) were observed, i.e., they looked colored with asubstantially even distribution of color ranging from white to black. Itis thought that this is because, as shown in FIG. 17(a), the liquidcrystal molecules 204′ are oriented in a direction generally parallel tothe interface with the polymer compound 202′, in other words, many ofthem are oriented in a direction parallel to the substrates 206′, 208′,and also the liquid crystal droplets 203′ are each oriented randomly ina plane parallel to the substrates 206′, 208′, thereby producing adelivery of color responsive to angles formed by the directions and apolarization axis of the polarizing plate.

It is presumed, therefore, that the liquid crystal droplets having aparticle size of 1-2 μm, as the liquid crystal display element of thisexample, presents a bipolar-form orientation pattern having nearly twopoles of orientation singular point. The then two poles are presumablyoriented randomly with respect to a three dimensional direction, becausethe liquid crystal droplets 203 are not so compressed as theabove-described liquid crystal droplets 203′.

On the other hand, when the observation of the same liquid crystaldroplets was made likewise under ambient temperature of 0° C., theliquid crystal droplets shown in FIG. 16(b) were observed, i.e., theylooked dark as a whole and also cross-like, black parts were observedwith respect to the direction of axis of polarization of the polarizingplate. It can be seen from this that the liquid crystal molecules in thevicinity of the interface with the polymer compound are oriented in adirection generally vertical to the said interface and many of them areoriented in a direction vertical to the substrates, as shown in FIG.17(b). It is presumed, therefore, that the liquid crystal dropletshaving a particle size of 1-2 μm, as the liquid crystal display elementof this example, presents a radial-form orientation pattern having apole at a center of each liquid crystal droplet.

Further, similar observations were made under differently variedtemperatures, the result showing that the liquid crystal molecularorientation took the bipolar-form under temperatures of about 5° C. ormore and took the radial-form under temperatures of 5° C. or less.

Next, the liquid crystal display element of this Example was measured inrespect of the electro-optical characteristics (appliedvoltage-transmittance characteristics) under ambient temperatures of 10°C. and 0° C. Specifically, a given driving circuit was connected withthe liquid crystal display element to apply a voltage, varyingcontinuously from 0 V to 20 V and from 20 V to 0 V, across the pixelelectrode 201 and the counter electrode 207 through the TFT elements,for making measurements of the liquid crystal display element in respectof the transmittance (intensity of transmitted light). The transmittancewas measured with the liquid crystal evaluating apparatus (LCD5000available from OTSUKA ELECTRONICS CO., LTD.). The measurement resultsunder ambient temperature of 10° C. are shown in FIG. 18(a) and themeasurement results under ambient temperature of 0° C. are shown in FIG.18(b). In these figures, the solid line represents transmittance at thetime of raised voltage and a broken line represents transmittance at thetime of dropped voltage.

When the optical hysteresis is defined as a percentage of a valueobtained by a maximum difference between the transmittance at the timeof raised voltage and that at the time of dropped voltage during theapplication of the same voltage being divided by the transmittance atthe time of application of 20 V, the optical hysteresis was as follows.In the case of the ambient temperature of 10° C. (in the case of thebipolar-form orientation pattern), the transmittance was as low as 1.5%.On the other hand, in the case of the ambient temperature of 0° C. (inthe case of the radial-form orientation pattern), the transmittance wasas significantly high as 20%. It is generally said in this respect thatthe optical hysteresis of not more than 2.0% can produce a good displayimage.

Further, when the optical hysteresis was measured under differentambient temperatures, good display characteristics were presented in therange of 10° C. to 85° C. It is therefore presumed that the orientationpattern in this temperature range is presumed to be of bipolar-form.

Gray scale was displayed to flash on and off at different levels bydifferent voltages being applied on and off. Under the ambienttemperature of 10° C., a good display with reduced residual image wasobtained, because of small optical hysteresis over the full levels ofgray scale. On the other hand, under the ambient temperature of 0° C.,the residual image remained outstandingly, so that, even when theflashing was stopped, the original gray scale was not reproduced. Hence,under the ambient temperature of 0° C., it is difficult for the liquidcrystal display element to be practically used.

As discussed above, the liquid crystal display element of very smalloptical hysteresis can be produced by allowing the liquid crystaldroplets to take the bipolar-form orientation pattern in the temperaturerange in which the liquid crystal display element is used.

Shown in this example is an example of the liquid crystal displayelement in which some neighboring liquid crystal droplets partiallyassociated with each other in series exist in the polymer matrix.Alternatively, the formation in which liquid crystal droplets areindividually separated from each other or the formation in which thepolymer matrix is formed in the network form and the liquid crystals areheld in between the networks of the polymer compound may be adopted toobtain the similar electro-optical characteristics.

Also, for the insulating film 205, either of the alignment layermaterial of polyimide type and that of polyamic acid type may be used.Further, inorganic insulating film may be used. Further, the insulatingfilms arranged are advantageous in that retention of voltage isenhanced, but are not necessarily indispensable.

In addition, monofunctional monomers and multifunctional monomers canproduce substantially the same effects as HDDA used as the additive.Particularly, bifunctional monomers, when used, allow the hysteresis tosignificantly reduce under low temperatures. The monofunctional monomerswhich may be used include, for example, isostearyl acrylate (LightAcrylate IS-A available from KYOEISHA CO., LTD.). The bifunctionalmonomers which may be used include, for example, triethylene glycoldiacrylate (3EG-A), PEG #200 diacrylate (4EG-A), PEG #400 diacrylate(9EG-A), neopentyl glycol diacrylate (NP-A), 1,6-hexandiol diacrylate(1.6 HX-A; all of them are available from KYOEISHA CHEMICAL CO., LTD.)or urethane acrylate (e.g. M-1100, M-1200, M-1210, M1310, or M-1600 allavailable from TOAGOSEI CO., LTD.) expressed by the aforesaid chemicalformula 1. The trifunctional acrylates which may be used include, forexample, trimethylpropane triacrylate (TMP-A) and pentaerythritoltriacrylate (PE-3A, all of them are available from KYOEISHA CHEMICALCO., LTD.). These materials may be used singly or in combination of twoor more kinds to reduce the hysteresis under low temperatures.

Also, combination of polymerizable monomer and liquid crystal materialis not limited to those disclosed above, but any combination will do, aslong as the polymerizable monomer in the liquid crystal polymerprecursor compatible solution is allowed to be copolymerized byirradiation of ultraviolet. In the case of the liquid crystal dropletsthen having the particle size in the range of from not less than 0.8 μmto not more than 2.5 μm, the liquid crystal display element havingexcellent scattering power can be produced. The particle size in therange of from not less than 1 μm to not more than 2 μm, in particular,can provide the result that the interval between the substrates isreduced so that the liquid crystal display element can be driven by alow voltage enough to drive the TFT elements easily.

The panel gap is not limited to 13 μm as disclosed above, but is simplyrequired to be not less than 5 μm. By letting the panel gap be in therange of from not less than 10 μm to not more than 15 μm, in particular,the driving voltage and the scattering power can be allowed to becompatible.

In addition, the intensity of ultraviolet need not be limited to 160mW/cm², but the intensity of ultraviolet of not less than 160 mW/cm² hasthe effect of allowing the optical hysteresis to be reduced under hightemperatures.

Further, the smaller the tilt angles, the better. The tilt angle set at5° produces, in particular, the great effect of maintaining thebipolar-form orientation pattern, though need not be limited thereto.The tilt angles of not more than 10° can produce the similar effect(stable bipolar-form orientation pattern).

Shown herein is an example of the liquid crystal display element whichis so formed as to allow the transition from the bipolar-formorientation pattern to the radial-form orientation pattern to begenerated under ambient temperature of about 5° C., so as to be usablein the temperature range of 10 to 85° C. A liquid crystal displayelement usable in a temperature range e.g. in the range of 0 to 85° C.can also be produced easily. In this case, in the process of the phaseseparation and polymerization caused by irradiation of ultraviolet toproduce the liquid crystal display element, the temperature of theliquid crystal panel at the time of irradiation of ultraviolet and theintensity of ultraviolet may be controlled and also the concentration ofadded monomer may be regulated to maintain the bipolar-form orientationpattern under the ambient temperature of 0° C. as well.

It is noted that the temperature range for a good display to bepresented depends on intended purposes of the liquid crystal displayelement. When the liquid crystal display element is used to a projectiondisplay, for example, it is commonly required that a lower limittemperature be not more than 10° C. at maximum and an upper limittemperature be higher than a temperature lower than a clearing pointtransition temperature of the liquid crystal by 5° C. When the liquidcrystal display element is used to a direct-view display or a reflectiondisplay, the lower limit temperature is desirably not more than 0° C.

In more detail, letting the clear point transition temperature of theliquid crystal display element be Tni, as long as surface temperature ofthe liquid crystal display element falls in the range of from not lessthan 10° C. to not more than Tni−5° C., the liquid crystal displayelement presents fully practicable performances even in a display withan intense back light such as the projection display. Also, when thelower limit temperature of the liquid crystal display element is notmore than 0° C., for example, the liquid crystal display element mayalso be used for a reflection display or a direct view display used to aportable terminal exposed to outside air temperature. Needless to say,the lower the lower limit of the operating temperature, the more usefulthe practicable performances.

Further, the element of little change in color can be obtained byletting the upper limit be 5° C. or less from the cleaning pointtransition temperature of the liquid crystal.

Example 2-2

The liquid crystal display element according to Example 2-2 ischaracterized in that the transition temperature, under which theorientation pattern is transformed from the bipolar-form to theradial-form, is reduced by letting the anchoring index under the ambienttemperature of 30° C. be not less than 0.7, whereby the opticalhysteresis under low temperatures is attempted to be reduced.

FIG. 19 is a sectional view of the liquid crystal display elementaccording to Example 2-2. The liquid crystal display element of thisExample is the same in mechanical constitution as the above Example 2-1,so that components of like function are given like reference numerals,and a description thereof will be omitted.

According to the liquid crystal element of this Example, the anchoringindex of (V90×R)/d is set at 1.1, where V90 is an applied voltagerequired for the transmittance to become 90% in the temperature ofelement of 30° C.; d is an interval between the counter substrate 256and the active matrix substrate 258; and R is an average particle sizeof liquid crystal droplets or an average interval of a three dimensionalnetwork form of matrix comprising polymer compound. In more detail, thevoltage V90 is an applied voltage required for the transmittance tobecome 90% when the alternating voltage of 30 Hz is applied across thepixel electrode 251 and the counter electrode 257 through the drivingcircuit 259. At this time, the liquid crystal molecular orientation inthe liquid crystal droplets 253 takes the bipolar-form orientationpattern in which the liquid crystal molecules 254 have a plurality oforiented electrodes in the vicinity of their interfaces with the polymercompound 252, and the liquid crystal molecules 254 around the centerpart of each liquid crystal droplet 253 are uniformly oriented along thedirection of an electric line of force.

The liquid crystal display element was produced in the same producingmethod, except that when the liquid crystal polymer precursor compatiblesolution was prepared,

(a) 1% of polymerization initiator (Benzyl Methyl Ketal available fromNIPPON KAYAKU CO., LTD.) and

(b) 2% of KS-HDDA of 1,6-hexandiol diacrylate (KAYARAD HDDA availablefrom NIPPON KAYAKU CO., LTD.) for controlling the interfacialrestrictive force were mixed.

The liquid crystal display element thus produced was measured in respectof the particle size of the liquid crystal droplets 253; the transitiontemperature for the orientation pattern to be transformed from thebipolar-form to the radial-form; and the electro-optical characteristics(applied voltage-transmittance characteristic) in the same manner as inExample 2-1, the results being that the average particle size R was 1.0μm; the transition temperature was −5° C.; and the optical hysteresisunder the ambient temperature of 10° C. was as small as 1.2%. Thus, theliquid crystal display element having a good display capability wasobtained.

Also, the anchoring index (V90×R)/d was 1.1, as aforesaid, whendetermined with reference to the particle size R; the applied voltageV90 required for the transmittance resulting from the appliedvoltage-transmittance characteristics to become 90%; and the interval dbetween the substrates 256, 258.

As a substitute for KS-HDDA of 1,6-hexandiol diacrylate for controllingthe interfacial restrictive force, 2% of fluoro -polymerizable-monomer(Light Acrylate FA108 available from KYOEISHA CHEMICAL CO., LTD.) wasadded to produce a similar liquid crystal display element. The liquidcrystal display element thus produced was measured in respect of theanchoring index under 30° C., the anchoring index being 0.6. Inaddition, the transition temperature was as high as 20° C. and theoptical hysteresis under the ambient temperature of 10° C. was as toolarge as 40% to be practicable.

Further, various kinds of liquid crystal display elements were producedwith variations in kinds of additives and concentration of theadditives, and were measured in respect of the electro-opticalcharacteristics and others to determine the relationship between theanchoring index and the orientation transition temperature. The resultsare shown in TABLE 2-1 and FIG. 20.

TABLE 2-1 Relationship between Anchoring Index and OrientationTransition Temperature Orientation Average particle transition size R ofLiquid temperature crystal droplets Anchoring No. (° C.) V90 d (μm)Index 1 27 3.23 12.4 1.38 0.36 2 27 3.93 12.7 1.33 0.41 3 22 4.46 12.11.28 0.47 4 25 4.54 12.6 1.39 0.50 5 28 4.90 12.7 1.36 0.52 6 18 5.5412.5 1.20 0.53 7 16 5.56 12.7 1.28 0.56 8 15 6.04 12.6 1.23 0.59 9 185.56 12.4 1.41 0.63 10 8 7.21 12.6 1.14 0.65 11 13 6.72 12.5 1.21 0.6512 15 6.83 12.6 1.29 0.70 13 9 7.43 12.6 1.24 0.73 14 9 7.53 12.6 1.250.75 15 3 7.70 12.6 1.24 0.76 16 13 8.74 12.4 1.08 0.76 17 11 8.92 12.61.09 0.77 18 0 10.67 12.5 1.01 0.86 19 −1 8.08 12.3 1.39 0.91 20 3 11.0612.5 1.06 0.94 21 0 10.76 12.6 1.12 0.96 22 −5 12.91 12.5 1.04 1.07

Shown by TABLE 2-1 and FIG. 20 is the correlation between the anchoringindex and the orientation transition temperature. With the anchoringindex set to be more than 0.7, the orientation transition temperaturewas brought to 10° C. or less, and the optical hysteresis under theambient temperature of 10° C. was as so low as about 2% or less, so thatthe liquid crystal display element having a good display capability wasproduced.

It is noted that the additives for controlling the interfacialrestrictive force are not limited to those disclosed above, but variouskinds of additives capable to allow surface energy of monomer toincrease may be used. Further, two or more kinds of additives may beused in combination. In this case, the surface energy of monomers comesto be the arithmetic mean of the influences of the additives, so thatthe control of the surface energy or the adjustment of the orientationtransition temperature is further facilitated. In addition, theconcentration of the additives is not limited to those disclosed above,but since even a small amount of additive generally provides a greateffect, a not more than 5% of additives can provide a sufficient effect.

Other forming materials and production conditions or requirements may bevaried, as described in Example 2-1.

Example 2-3

The liquid crystal display element according to Example 2-3 ischaracterized in that the liquid crystal display element is producedwith the temperature of the liquid crystal panel at the time ofirradiation of ultraviolet kept higher than the thermal separationtemperature of the liquid crystal polymer precursor compatible solutionby 3-15° C., whereby the transition temperature under which theorientation pattern is transformed from the bipolar-form to theradial-form is lowered, for making attempts to reduce the opticalhysteresis under low temperatures.

The mechanical constitution of the liquid crystal display element ofthis Example 2-2 is similar to that of the above Example 2-3.

The liquid crystal display element is produced in the following manner.

FIG. 21 is a schematic view showing the structure of a productionapparatus of the liquid crystal display element.

In the production apparatus, as shown in FIG. 21, a liquid crystal panel280 filled with the liquid crystal polymer precursor compatible solutionis mounted on a base 281 connected to a circulating thermostatic chamber282, through a reflecting plate 286, so that the surface temperature ofthe liquid crystal panel 280 is controllably set at a desiredtemperature. An ultraviolet irradiating apparatus 283 is located overthe base 281 so that the liquid crystal panel 280 can be irradiated withultraviolet through an ultraviolet filter 284 peaking at an absorptionwavelength of 350 nm and supported by a support member 285. Thereflecting plate 286 is made of aluminum, for example, so that theultraviolet irradiated by the ultraviolet irradiating apparatus 283 canwork effectively.

The liquid crystal panel 280, filled with liquid crystal polymerprecursor compatible solution similar to that of Example 2-1, wasirradiated with ultraviolet of intensity of 120 mW/cm² for 30 seconds byuse of the production apparatus, to produce the liquid crystal displayelement. Prior to the irradiation of ultraviolet, a thermal phaseseparation temperature of the liquid crystal polymer precursorcompatible solution was measured with the mettler, the result being 10°C. Accordingly, the irradiation of ultraviolet was made, with thetemperature of the liquid crystal panel 280 kept at 18° C. higher thanthe thermal phase separation temperature by 8° C.

The liquid crystal display element thus produced was measured in respectof the average particle size of the liquid crystal droplets 253; thetransition temperature for the orientation pattern to be transformedfrom the bipolar-form to the radial-form; and the electro-opticalcharacteristics (applied voltage-transmittance characteristic) in thesame manner as in Example 2-1, the results being that the transitiontemperature was as low as 7° C.; and the optical hysteresis under theambient temperature of 10° C. was as so small as 1.0%. Thus, the liquidcrystal display element having a good display capability was obtained.

On the other hand, when the liquid crystal panel 280 was irradiated withultraviolet under the same conditions, except that the temperature ofliquid crystal panel 280 was kept at 12° C. higher than the thermalphase separation temperature by 2° C., to produce a liquid crystaldisplay element, the transition temperature was 18° C. and the opticalhysteresis under the ambient temperature of 10° C. was as so large as15%. Thus, the liquid crystal display element thus produced failed tohave a good display capability.

Further, with the liquid crystal panel 280 varied in temperature, themeasurements of the transition temperature and the anchoring index weremade, the results being as shown in TABLE 2-2. From the same TABLE it isseen that setting the temperature of the liquid crystal panel 280 at atemperature higher than the thermal phase separation temperature by3-15° C. enables the transition temperature for the orientation patternto be transformed from the bipolar-form to the radial-form to be reducedand in turn enables the optical hysteresis under low temperatures to bereduced. In addition, setting a 7-12° C. higher temperature can providesimilar effects and also enables the liquid crystal droplets to beprevented from increasing in particle size.

TABLE 2-2 Relationship between Polymerization Temperature and AnchoringIndex Average Orienta- Polymeri- particle size tion zation R of Liquidtransition Tempera- crystal tempera- ture ΔT Anchoring droplets tureEvalua- No. (° C.) (° C.) Index (μm) (° C.) tion 1 12 2 0.05 0.98 18 X 213 3 0.6 0.99 15 Δ 3 16 6 0.63 1.02 12 Δ 4 18 8 0.85 1.36 7 ◯ 5 23 130.97 1.49 0 ⊚ 6 25 15 1.0 1.70 −2 ⊚ ΔT = Thermal phase separationtemperature (10° C. in common) − Panel temperature at the time of UVirradiation, and Anchoring index = V90 · R/d

The intensity of ultraviolet need not be limited to 120 mW/cm², but anot less than 100 mW/cm² intensity of ultraviolet can provide similareffects and can contribute to production of uniform elements with littleunevenness in particle size caused by scratch defects of the glasssubstrate and things like that.

Though the time for irradiation of ultraviolet is preferably 30 secondsor less, a longer than 30 seconds irradiation is also acceptable.However, a more than 5 minutes irradiation causes decomposition ofliquid crystals to present a challenge for reliability of a retention ofvoltage and others, so that a shorter than 5 minutes irradiation isdesirable.

Absorption wavelength of the ultraviolet filter 284 is not limited to350 nm. Any suitable absorption wavelength, e.g. 360 nm or 370 nm, maybe selected so that the polymer is polymerized properly without causingdecomposition of the liquid crystals, allowing for absorptionwavelengths of the liquid crystals and polymer.

The interval between the ultraviolet filter and the liquid crystal panelshould preferably be set at 1 mm or more in order to prevent temperaturerise of the liquid crystal panel. On the other hand, in order to preventultraviolet from running into the liquid crystal panel from around theultraviolet filter to hinder the progress of uniform polymerization, theinterval should preferably be within 2 cm at maximum. More preferably,the interval should be in the range of 3 mm or more to 1 cm or less toproduce the liquid crystal display element capable to surely suppresstemperature rise and uniform in the degree of polymerization. Of course,the ultraviolet filter is required to have a larger size than the liquidcrystal panel. To be more specific, the ultraviolet filter of forexample 1.2 times or more as large as the liquid crystal panel caneasily prevent the ultraviolet running into the panel around the filter,though depending on the interval between the filter and the liquidcrystal panel.

The reflecting plate made of aluminum is taken as an example, but thereflecting plate may be made of anything of high reflectivity such asaluminum foil and the like.

The circulating thermostatic chamber, which is used for controlling thetemperature of the liquid crystal panel, may be structured such that theentirety of the apparatus can be arranged in it. Also, a Peltier elementand the like may be used. In addition, the liquid crystal panel may beprovided at its each side with a control plate guided from thecirculating thermostatic chamber, to make the temperature control fromthe both sides of the panel. Further, the liquid crystal panel may beprovided at a surface thereof with a temperature sensor such as athermocouple which is in turn connected with a feedback system, thecirculating thermostatic chamber or the like, to automate thetemperature control. This can facilitate the temperature control of theliquid crystal panel with more accuracy.

Other forming materials and production conditions or requirements may bevaried, as described in Example 2-1.

(3) Examples of Third Inventive Group

Described below is the specific content of the invention of the thirdinventive group. First, a summery of the polymer dispersion type liquidcrystal display element directed to the third inventive group isoutlined with reference to FIG. 26. Polymer compound 302 and liquidcrystal droplets 303 are placed with being dispersed in between glasssubstrates 300 having transference electrodes 301, and the liquidcrystal droplets 303 are scattered in the polymer compound 302 in theisland form. The liquid crystal molecules 304 in the liquid crystaldroplets 303 take a bipolar-form orientation pattern with two poles inthe vicinity of walls of the liquid crystal droplets 303. In FIG. 26,the liquid crystal droplets 303 are illustrated to be individuallyseparated from each other, but some neighboring liquid crystal dropletsmay be in the form of being jointed to each other with partiallycontacting with each other. In addition, a polymer network type liquidcrystal may be adopted in which the polymer compound 302 is formed intoa network form so that the liquid crystal droplets can be held inbetween the networks.

Description on Examples will be given below.

Example 3-1

Example 3-1 is directed to a polymer dispersion type liquid crystaldisplay element which is structured so that capacitance ratio of thecapacitance-voltage characteristics can be 60% or more with a voltagerequired for the transmittance of the voltage-transmittancecharacteristics to be 10% or more. This element was produced in thefollowing steps and conditions.

It is noted that the capacitance ratio indicates a value defined by thefollowing expression.

Capacitance ratio %=(capacitance for the case of any selected voltagebeing applied to the element/a maximum value of the capacitance for thevoltage applied to the element)×100  Expression 3-3

Production Conditions

(1) 90 wt % of polymerizable monomer (2-ethylhexyl acrylate), 9 wt % ofoligomer (Biscoart 828 available from OSAKA ORGANIC CHEMICAL INDUSTRY)and 1 wt % of polymerization initiator (Benzyl Methyl Ketal availablefrom NIPPON KAYAKU CO., LTD.) were mixed to produce the polymerprecursor mixture. 80 wt % of liquid crystal material of TL205(available from Merck Japan Limited) was added to 20 wt % of the thusproduced mixture to prepare liquid crystal polymer precursor compatiblesolution.

(2) An alignment layer material was printed on the glass substrate 300having the transference electrode 301 by the printing method and thenwas cured in an oven to form an insulating film 305.

(3) After a similar insulating film was formed on a glass substrate 306having a transference electrode 307, the glass substrates 300, 306 werelaminated to each other through glass spacers at an interval of 13 μm.OPTOMER AL8534 (available from JAPAN Synthetic Rubber Co., Ltd.) wasused as the above alignment layer material. Also, a glass plate 1737available from CORNING INC. (1.1 mm in thickness) was used as the glasssubstrate.

(4) The compatible solution was injected in between the laminatedsubstrates (hereinafter it is referred to as “the panel”) via a vacuuminjection method, to produce a liquid crystal panel.

(5) After a 350 nm filtering filter was laminated on the liquid crystalpanel, the temperature of liquid crystal panel (polymerizationtemperature) was set at 13° C. Then, the panel was irradiated withultraviolet of intensity of 120 mW/cm² for 30 seconds to allow thepolymerizable monomer to be polymerized, to thereby produce the polymerdispersion type liquid crystal display element of Example 3-1. Theintensity of ultraviolet was a value measured at a point on the surfaceof the panel via an ultraviolet illuminance meter (UV-M02 available fromOAK MANUFACTURING CO., LTD.).

Evaluation of the element

The driving circuit was connected to the element separately, for makingmeasurements of the optical hysteresis and the capacitance hysteresis.The measurements were made under conditions of the applied voltage of 30V at maximum and the frequency of 300 Hz. The temperature range was inthe range of 0° C. to 60° C. The measurements were made in the samemeasuring apparatus and method as those in Example 1-1.

Shown in FIG. 22 is the measurement results under 30° C. As seen fromFIG. 22, the voltage to provide a 10% transmittance (a percentage formaximum transmittance quantity) was 4.47V and the capacitance ratio atthat voltage was 60%. The optical hysteresis in the process of raisedvoltage and in the process of dropped voltage at that voltage, whenmeasured, was as small as 1.9%. Further, from the check on the presenceand absence of the residual image resulting from the hysteresis via theflash-on-and-off display, it was confirmed that there presented littleresidual image.

For further detailed measurements on the relationship between theoptical hysteresis (%) and the capacitance ratio, similar elements wereproduced, with an additive having an anchoring strength adjustingcapability added to the compatible solution of Example 3-1 or withvaried intensity of ultraviolet. These elements were measured in respectof the capacitance ratio and the optical hysteresis in a similar mannerto the above.

Shown in TABLE 3-3 are the production conditions as well as themeasurement results. The measurement results are plotted in FIG. 27,plotting the optical hysteresis against the capacitance ratio under thetransmittance of 10%. It is seen from FIG. 27 that a not more than 2%optical hysteresis requires that the capacitance ratio under thetransmittance of 10% be set 60% or more, and a not more than 1% opticalhysteresis requires that the capacitance ratio under the transmittanceof 10% be set 65% or more.

TABLE 3-3 Composition of Liquid crystal polymer precursor UV IntensityCapacitance Optical No. compatible solution mW/cm² ratio (%) hysteresis1 8.2 wt % of FM108 120 64.5 1.5 added (N.B.) 2 Example 3-1 120 60.0 1.93 2% wt % of HDDA 120 57.5 3.8 added (N.B.) 4 2 wt % of FM108 added 25067.0 0.8 (N.B.) N.B.) Added to the compatible solution of Example 3-1;HDDA: KARARAD · available from NIPPON KAYAKU CO., LTD.; FM108: LightAcrylate FM108 · available from KYOEISHA CHEMICAL CO., LTD.; No. 2 isExample 3-1

Example 3-2

Produced in the Example 3-2 was the polymer dispersion type liquidcrystal display element of which capacitance hysteresis Chys under theelement driving temperature of 30° C. was not more than 1.5% at maximum.The fact that the produced liquid crystal display element had the abovecharacteristic was confirmed by use of the technique described inExample 3-1. The production was conditioned on the temperature of liquidcrystal panel (polymerization temperature) in the phase separationoperation being set at 13° C. and on the panel being irradiated withultraviolet of 120 mW/cm² for 30 seconds for the phase separation. Otherconditions are the same as those of Example 3-1.

Example 3-3

Produced in the Example 3-3 was the polymer dispersion type liquidcrystal display element of which capacitance hysteresis Chys in theapplied voltage required for the optical hysteresis to become a maximumvalue under the element driving temperature of 30° C. was not more than0.2%. The fact that the liquid crystal display element of this Example3-3 also had the above characteristic was confirmed by the same manneras the above.

The production was conditioned on the temperature of liquid crystalpanel (polymerization temperature) in the phase separation operationbeing set at 17° C. and on the panel being irradiated with ultravioletof 200 mW/cm² for 30 seconds for the phase separation. Other conditionsare the same as those of Example 3-1.

Other matters

Insulating film forming materials are not necessarily limited to thosedescribed in the above Examples, but may include either of those ofpolyimide type and those of polyamic acid type. Again, inorganicmaterials including SiO₂ may be used. Further, an additive may be usedto change the anchoring strength in the above Examples. The additiveswhich may be used include bifunctional monomers such as HDDA (KAYARADHDDA available from NIPPON KAYAKU CO., LTD.), and some wt % of additivesmay be added to allow the interface anchoring to increase. On the otherhand, some wt % of fluoro -polymerizable-monomer (Light Acrylate FA108available from KYOEISHA CHEMICAL CO., LTD.) may be used to allow theinterface anchoring strength to decrease.

Also, combination of the liquid crystal.polymer composition is notlimited to those disclosed in Examples above. Any general combinationwill do, as long as it can allow the liquid crystal and the polymer tobe mixed and also be copolymerized by irradiation of ultraviolet. Inthis case, the average particle size of the liquid crystal droplets inthe range of from not less than 0.8 μm to not more than 2.5 μm canprovide the element having an excellent scattering power. In particular,those in the range of from not less than 1 μm to not more than 2 μm canallow the liquid crystal panel to be driven with a low voltage enough todrive the TFT by combining with the panel gap.

The panel gap is not limited to that disclosed in the Examples above,but is simply required to be not less than 5 μm. By letting the panelgap be in the range of from not less than 10 μm to not more than 15 μm,in particular, the driving voltage and the scattering power can beallowed to be compatible.

The intensity of ultraviolet need not be limited to those disclosedabove, but a not less than 100 mW/cm² intensity of ultraviolet cancontribute to production of uniform elements without making scratchdefects of the glass substrate and the like prominent. In particular, anot less than 150 mW/cm² intensity of ultraviolet is effective forreduction in optical hysteresis under high temperatures.

As a substitute for the glass substrates with transference electrodesare used for the upper and lower substrates of the liquid crystal panelin the above Examples, the TFT type liquid crystal display panel inwhich a number of active matrix elements are formed on the glasssubstrates may, of course, be used to provide similar effects.

(4) Examples of Fourth Inventive Group

Example 4-1

This Example is an example directed to the 65^(th) to 69^(th) aspects ofthe fourth inventive group.

Poly-L-sodium glutamate, which is an example of polyamino acidderivatives, was first used as a starting material, and carboxyl partswere modified with diamine, whereby various kinds of insulating paintfilm materials different in surface tension were synthetically preparedin accordance with the following order. First, an 1% aqueous solution,by weight, of Poly-L-sodium glutamate was prepared and then wasneutralized with a 10% aqueous solution, by weight, of hydrochloricacid. Thereafter, poly-L-glutamic acid was released therefrom. Then, a5% solution, by weight, of chloroform containing any one kind ofprepared-in-advance methylenediamine materials, includingtrimethylenediamine, hexamethylenediamine and decamethylenediamine, wasadded with fully stirred, and the resulting mixed solution was allowedto stand. Then the mixed solution was separated into three layers. Theintermediate layer was dispensed out of these separated layers and wasdissolved with adding N,N-dimethyl formamide, to prepare insulatingpaint film materials of Example 1 (properly speaking, Example 4-1-1,though abbreviated like this) to the same 5 and of Comparative Example 1(which is also abbreviated as in the case of the Examples) to the same2, as shown in TABLE 4-1.

(TABLE 4-1) Insulating paint film material Liquid crystal ThresholdResponse Methylen material characteristics time diamine γ P (20° C.)Mate- γ LC (20° C.) γ value (20° C.) materials dyne/cm rial dyne/cm (20°C.) ms Compara Trimethylene 27.9 A 29.2 1.70 82.8 Ex. 1 diamine Ex. 1Hexamethylene 29.3 A 29.2 1.98 63.2 diamine Ex. 2 Decamethylene 32.5 A29.2 3.23 149.9 diamine Compara Hexamthylene 29.3 B 31.6 1.58 109.9 Ex.2 diamine Ex. 3 Decamethylene 32.5 D 31.6 2.19 73.2 diamine Ex. 4Hexamthylene 29.3 C 27.3 2.51 107.3 diamine Ex. 5 Hexamethylene 29.3 D29.8 1.72 68.2 diamine

The support substrate 412 forming on an inner surface thereof thetransference electrode 413 was prepared, and each of the insulatingpaint film materials of the Examples and the Comparative Examples wasapplied on the transference electrode 413 of the support substrate 411and 412 through the adoption of a spinner coating and then was driedunder temperature of 150° C. for 1 hour, to form the insulating paintfilm 414. The spinner was then conditioned on 500 rpm-10 sec./1500rpm-30 sec, in either case of which the produced film was about 100 nmin thickness.

Next, the insulating paint films 414 made of the respective insulatingpaint film materials shown in the Examples and Comparative Examples weremeasured in respect of the critical surface tension γp by the Dismanplotting method, using a wettability testing agent (available fromNAKARAI TESK CO., LTD.). The measurement results on the critical surfacetension γp obtained under the temperature of 20° C. are noted in TABLE4-1.

Further, four kinds of liquid crystals A-D, which were so prepared as tobe different in surface tension γLC from each other, were prepared andwere added to compositions each comprising lauryl acrylate as a matrixform polymer compound forming monomer (available from KYOEISHA CHEMICALCO., LTD.), M6100 as oligomer (available from TOAGOSEI CO., LTD.) andIrgacure 651 as a photo polymerization initiator (available fromCIBA-GEIGY LTD.) with fully stirred, to prepare polymerizablecompositions which develop into polymer dispersion type liquid crystals417. The surface tension γLC of each of the liquid crystals A-D underthe temperature of 20° C. is as shown in TABLE 4-1.

It is proven from combination of the critical surface tensions γp of theinsulating paint films 414 shown in Examples and Comparative Examplesand the surface tensions γLC of the liquid crystals A-D that: theinsulating paint film 414 of Comparative Example 1 combined with theliquid crystal A and the insulating paint film 414 of ComparativeExample 2 combined with the liquid crystal B (in the following FIGS.they are abbreviated to Compara. 1, Compara. 2) do not meet any one ofthe conditional expressions {circle around (1)}-{circle around (3)}; theinsulating paint film 414 of Example 1 combined with the liquid crystalA and the insulating paint film 414 of Example 3 combined with theliquid crystal B (in the following FIGS. they are abbreviated to Ex. 1,Ex. 3) meet any one of the following conditional expressions {circlearound (1)}-{circle around (3)}; and the insulating paint film 414 ofExample 2 combined with the liquid crystal A and the insulating paintfilm 414 of Example 4 combined with the liquid crystal C. (in thefollowing FIGS. they are abbreviated to Ex. 2, Ex. 4) meet theconditional expression {circle around (1)}, while the insulating paintfilm 1 of Example 5 combined with the liquid crystal D (in the followingFIGS. it is abbreviated to Ex. 5) meets the conditional expression{circle around (2)} only. It is noted that meeting the above conditionalexpression {circle around (1)} means meeting the requirement of γLC−γp<0(Expression 4-1). Also it is noted that meeting the conditionalexpression {circle around (2)} means meeting the requirements of bothγLC−γp<0 (Expression 4-1) and −1·dyne/cm <γLC−γp (Expression 4-2) ormeeting the requirements of 0<γLC−γp<1·dyne/cm (Expression 4-3).Further, it is noted that meeting the conditional expression {circlearound (3)} means meeting the requirements of both γLC−γp<0 (Expression4-1) and 0<γLC−γp>1·dyne/cm (Expression 4-3). (The above definitions arealso applied to the following.)

Further, the prepared polymerizable compositions were fully stirred andthereafter were injected in empty cells (not shown) separately arrangedin the inside of a closed container comprising a pair of opposingsubstrates 411. Then, the resulting cells were irradiated withultraviolet of 365 nm (about 25 mW/cm²) for 100 seconds under thetemperature of 20° C. The polymerizable compositions in the respectiveempty cells were then polymerized by the irradiation of ultraviolet togrow into the polymer dispersion type liquid crystals 417, resulting incompletion of the liquid crystal display elements each having a mainstructure shown in FIG. 28.

The liquid crystal display elements formed in accordance with theabove-described steps were each measured in respect of the γ valueshowing steepness of the threshold and the response time, themeasurement results being as shown in TABLE 4-1 and FIGS. 29 and 30.FIG. 29 is a graph showing the relationship among the subtractionresults of γLC−γp, the γ value and the response time, and FIG. 30 is agraph showing the relationship between the γ value and the responsetime.

Specifically, the measurement results shows that Comparative Example 1presented the γ value, showing steepness of the threshold, of 1.70 andthe response time of 82.8 ms; Example 1 presented the γ value of 1.98and the response time of 63.2 ms; Example 2 presented the γ value of3.23 and the response time of 149.9 ms; Comparative Example 4 presentedthe γ value of 1.58 and the response time of 109.9 ms; Example 3presented the γ value of 2.19 and the response time of 73.2 ms; Example4 presented the γ value of 2.51 and the response time of 107.3 ms; andExample 5 presented the γ value of 1.72 and the response time of 68.2ms. Then, the measurement results show that Comparative Example 2 didnot present improved response time, nor did Examples 2 and 4 presentimproved response time due to the γ value increasing so excessively. Incontrast to this, Examples 1 and 3 meeting all of the above conditionalexpressions {circumflex over (1)}-{circumflex over (3)} and Example 5meeting the conditional expression {circumflex over (2)} presentedconsiderably improved response time as a consequence of optimization ofthe γ value.

Further, it is particularly noted from the measurement results that goodresponse time was provided in Example 1 presenting the γ value, showingsteepness of the threshold, of 1.98 and Example 3 presenting the γ valueof 2.19. In Examples 2 and 4 meeting the conditional expression{circumflex over (1)}, apparently the response time was not improved somuch, but temperature dependency was improved as discussed later. Also,the measurement results at that time showed that Comparative Example 1presented improved response time due to the optimization of the γ value,but presented no improvement of temperature dependency, as discussedlater.

Next, the liquid crystal display elements of Examples were measured inrespect of temperature dependencies including driving voltage, theresult being as shown in TABLE 4-2 and FIG. 31. FIG. 31 is a graphshowing a relationship between the subtraction result of γLC−γp and ΔVwhich is indexing value for expressing the temperature dependency. Theindexing value of ΔV was determined by:

ΔV(%)={(V MAX−V MIN)/V30}×100,  (Expression 4-6)

where V30 is the driving voltage of the liquid crystal display elementunder the temperature of 30° C., and V MAX and V MIN are the highestdriving voltage and the lowest driving voltage of the driving voltagesunder the temperatures of 20° C., 30° C. and 40° C., respectively. Thisevaluation shows that the smaller the ΔV, the better the temperaturedependency.

(TABLE 4-2) 20° C. 30° C. 40° C. Δ V V90 V90 V90 (%) Compara. 1 10.459.85 8.32 21.62 Ex. 1 11.45 12.71 11.98 9.91 Ex. 2 19.99 20.27 20.512.56 Compara. 2 10.20 8.75 6.87 38.05 Ex. 3 13.55 14.42 13.03 9.63 Ex. 418.05 18.77 19.34 6.87 Ex. 5 12.22 13.50 13.00 9.48

The results showed that Comparative Example 1 presented the ΔV of 21.62%and Comparative Example 2 presented the ΔV of 38.05%, so both of themfailed to provide good temperature dependency. On the other hand,Examples 1 and 3, both meeting all of the conditional expressions{circumflex over (1)}-{circumflex over (3)}, presented the ΔV of 9.91%and 9.63%, respectively; Examples 2 and 4, both meeting the conditionalexpression {circumflex over (1)}, presented 2.56% and 6.87%; and Example5, meeting the conditional expression {circumflex over (2)}, presented9.48%, from which it is seen that all Examples ensured good temperaturedependency. Further, it is also seen from the result that Examples 2 and4 comprising an insulating paint film made of an insulating paint filmmaterial capable of meeting the above conditional expression {circumflexover (1)} provided considerably improved temperature dependency. Themeasurements on the response time and the temperature dependency weremade by use of LCR-5000 available from OTSUKA ELECTRONICS CO., LTD.

Incidentally, the insulating paint film materials which may be usedinclude poly-L-sodium glutamate, which is an example of polyamino acidderivatives, used in the Examples, though need not be limited thereto,of course. Specifically, the insulating paint film materials which maybe used include polyamino acid itself or other polyamino acidderivatives including polyaspartic acid polyhistidine, polyarginine,polylysine and polyalanine; proteins including particularly myoglobin,haemoglobin, globulin, chymotrypsin and albumin which are polymercompounds with amino acid residue bonded thereto through peptide; andpolyimide base materials.

On the other hand, the oligomers and the monomers for forming thepolymer compound of matrix form are simply required to be polymerized bylight or heat in the presence of polymerization initiators. Theoligomers which may be used include polyurethane acrylate, polyesteracrylate and epoxy acrylate.

The monomers which may be used include not only commercially availableacrylic base monomers, such as 2-ethylhexyl acrylate, 2-hydroxyethylacrylate, neopentyl glycol diacrylate, hexanedioldiacrylate, diethyleneglycol diacrylate, tripropylene glycol diacrylate, polyethylene glycoldiacrylate and trimethylolpropane triacrylate but also commerciallyavailable ones other than the acrylic base monomers. In addition, thepolymerization initiator used is not limited to Irgacure 651 but may beselectively combined with Darocure 1173, Darocure 4265 and Irgacure 184available from CIBA-GEIGY LTD.

Furthermore, the insulating film need not be limited to the paint film,as long as it can provide insulation. For example, a film attached tothe electrode by other suitable means, such as a deposited film, may beused.

Similarly, the counter substrate, the electrode and the insulating paintfilm need not be precisely identical in size, shape and material totheir counterparts, of course.

Example 4-2

This Example is an example directed to the 60^(th) aspect to the 77^(th)aspect of the fourth inventive group.

FIG. 32 is a schematic illustration of the structure in section of thepolymer dispersion type liquid crystal element of this Example, which isnot essentially different from FIG. 28 concerning Example 4-1. In theFIG., 411 denotes a counter substrate, on which a transference electrode413 and an insulating paint film 414 are formed. 412 denotes a glasssubstrate, on which TFT (not shown), the transference electrode 413 andthe insulating film 414 are formed. Injected in a space between thecounter substrate 411 and the glass substrate 412 is the polymer.liquidcrystal material complex 417, which has a structure of the droplets 416of liquid crystal being dispersed in the polymer compound 415.

In FIG. 32, droplets 416 of the liquid crystal are independentlyinterspersed in an island form in the polymer compound 415, but are notso limited but is susceptible to various forms. For example, the liquidcrystal droplets interspersed may be partially associated in series withneighboring droplets. Alternatively, the polymer compound 415 may beformed into a network form, in the networks of which the liquid crystaldroplets are held with interspersed.

The above-described polymer dispersion type liquid crystal element wasproduced in the following manner.

(1) 60% of polymerizable monomer (2-ethylhexyl acrylate), 39% ofpolymerizable oligomer having imino group (Urethane acrylate; M-1600available from TOAGOSEI CO., LTD.) and 1% of Benzyl Methyl Ketal aspolymerization initiator (available from NIPPON KAYAKU CO., LTD.) weremixed, to form the polymer precursor solution. Then, 80% of liquidcrystal material having a 30 dyne/cm surface tension γLC (MT5524available from CHISSO PETROCHEMICAL CORPORATION) as measured by ahanging drop method (24° C.) was added to 20% of the thus obtainedpolymer precursor solution, to produce liquid crystal polymerprecursor.compatible solution.

(2) On the other hand, the transference electrode 413, a source line, agate line and others were provided for the glass substrate 412 of the1737 substrate (1.1 mm in thickness) available from CORNING INC. throughthe techniques of vacuum deposition and etching to thereby produce anactive matrix substrate. Further, OPTOMER AL8534 (available from JAPANSynthetic Rubber Co., Ltd.) was printed on the substrate and then wascured in an oven, to form insulating paint film 414 thereon.

(3) After the insulating film 414 was formed on the counter substrate411 having the transference electrode 413 in a similar manner, the glasssubstrate 412 and the counter substrate 411 were laminated to each otherthrough glass spacers at an interval of 13 μm.

(4) The polymer precursor. liquid crystal mixture was injected inbetween the laminated substrates and thereafter was irradiated withultraviolet of 365 nm in wavelength and 95 mW/cm² in intensity to allowthe polymerizable polymer precursor (monomer and oligomer) to bepolymerized. By doing this, the polymer dispersion type liquid crystaldisplay element arranging therein polymer-liquid crystal complex inwhich the liquid crystal droplets are dispersed in the polymer compoundwas completed.

Next, a power source was connected to the polymer dispersion type liquidcrystal element thus produced, and a voltage was applied across thecounter electrode and the pixel electrode through the drive of TFT tomake measurements on the temperature dependency of the voltage-opticalcharacteristics. To be more specific, letting V90% be an applied voltagerequired for the panel transmittance to become 90%, values on the V90%were measured under temperatures −10° C., 0° C., 10° C., 20° C., 30° C.,40° C., 50° C. and 60° C. The panel transmittance was measured by use ofa liquid crystal evaluating apparatus (LCD5000 available from OTSUKAELECTRONICS CO., LTD.).

Then, the temperature dependency index ΔV in Expression 4-7 shown belowwas defined to make evaluations on the panel transmittancecharacteristics in their relation with the temperatures through the usesof the measured values on the V90%. In Expression 4-7, Vmax represents amaximum value of V90% under temperature in the range of from 0° C. to60° C.; Vmin represents a minimum value of V90% under temperature in therange of from −10° C. to 60° C.; and ³⁰V90% represents the value of V90%under the temperature of 30° C.

ΔV=(Vmax−Vmin)/³⁰V90%  Expression 4-7

On the other hand, the measurements on the critical surface tension γPof the polymer compound forming the polymer.liquid crystal complex ofthe polymer dispersion type liquid crystal display element thus producedwere made, to determine a holding relationship between the criticalsurface tension γP and the surface tension γLC.

The measurements of the critical surface tension γP of the polymercompound were made in the following manner. First, the counter substrate411 was peeled off from the polymer dispersion type liquid crystalelement, and then the polymer compound was washed with isopropyl alcoholto eliminate the liquid crystals from its surface and dried by blowingnitrogen against it. Thereafter, five different kinds of wettabilityindexing standard solutions (available from NAKARAI TESK CO., LTD.) Nos.31, 34, 37, 42 and 46 were dropped on the washed surface of the polymercompound to measure the contact angles θ. Then, laying off cos θ asabscissa and a surface tension γ of the wettability indexing standardsolution as ordinate, γ to take cos θ=1 is determined and the γ isdefined as the critical surface tension γP (Disman plotting method). Themeasurements on the critical surface tension γP of the polymer compoundand the surface tension γLC of the liquid crystal were made with anautomatic measuring apparatus available from KYOWA KAIMEN CHEMICAL CO.,LTD.

Result

The measurement result on the V90% is shown in FIG. 33, and themeasurements on the temperature dependency index ΔV, the surface tensionof the liquid crystal and the critical surface tension γP of the polymercompound are shown in TABLE 4-3 given below. It is to be noted that thecharacteristic feature of the liquid crystal display element of thisExample is in that the liquid crystal having the 30 dyne/cm surfacetension and the polymerizable oligomer (urethane acrylate) having iminogroup having 32 dyne/cm critical surface tension γP are used incombination.

Example 2-1

As evident from the results shown in TABLE 4-3 given below and FIG. 33,according to the liquid crystal display element of Example 2-1 (properlyspeaking, Example 4-2-1, though abbreviated like this), the γP>γLC heldbetween the critical surface tension γP of the polymer compound and thesurface tension γLC of the liquid crystal. In addition, it was foundthat a V90%-Temperature curve peaked at the vicinity of 22° C. and thetemperature dependency index was as small as 0.21.

(TABLE 4-3) Critical surface tension of polymer Surface tension compoundof liquid crystal Temperature γ P γ LC dependency index (dyne/cm)(dyne/cm) Δ V Compara. 2-1 32 30 0.21 Ex. 2-2 31 30 0.25 Ex. 2-3 31 300.22 Compara. 2-4 33 30 0.22 Ex. 2-5 32 30 0.25 Ex. 2-6 32 30 0.22Compara. 1 25 30 0.50

Example 2-2

Except that M-1200 (Urethane acrylate) (available from TOAGOSEI CO.,LTD.) was used as the polymerizable oligomer having imino group, thepolymer dispersion type liquid crystal display element was produced in asimilar manner to in the abovesaid Example 2-1, and the samemeasurements as those in the Example 2-1 were made. The measurementresults are shown in FIG. 34 and TABLE 4-3 given above.

Result

As seen from TABLE 4-3 above, the critical surface tension γP of thepolymer compound was 31 dyne/cm and the γP>γLC held in this Example 2—2also. Also, according to the liquid crystal display element of thisExample 2—2, the V90% increased as temperature rose, but the temperaturedependency index was as small as 0.25, making little difference overthat of the above Example 1, as seen from the results shown in TABLE 4-3and FIG. 34.

The characteristic feature of the liquid crystal display elementaccording to this Example 2—2 is in that M-1200 available from TOAGOSEICO., LTD. was used. The difference between M-1200 and the M-1600 used inthe above Example 1 is in that M-1200 has a different chemical structureexpressed by chemical formula 1 in R, R′ and polyol and has a highermolecular weight.

CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1

where n=an integer.

Example 2-3

Except that the polymerizable oligomer having hydroxyl group (Urethaneacrylate; M-233 available from TOAGOSEI CO., LTD.) was used, all werethe same as those in Example 2-1 above. The same measurements as inExample 2-1 above were made. The results are shown in FIG. 35 and TABLE4-3 given above.

Result

As seen from TABLE 4-3 above, the critical surface tension γP of thepolymer compound was 31 dyne/cm and the γP>γLC held in this Example 2-3also. Also, as seen from the results shown in TABLE 4-3 and FIG. 35, theV90%-temperature curve peaked around 15° C. On the other hand, thetemperature dependency index was as small as 0.22, making littledifference over that of the above Example 1. The characteristic featureof the liquid crystal display element according to this Example 2-3 isin the use of the polymerizable oligomer having hydroxyl group.

Example 2-4

Except that the polymerizable oligomer having imino group (Urethaneacrylate; UF-8001 available from Kyoeisha Kagaku Kogyo K.K.) was used,all were the same as those in Example 1 above. The dispersion typeliquid crystal display element was produced and the same measurementswere made as in Example 2-1. The measurement results are shown in FIG.36 and TABLE 4-3 given above.

Result

As seen from TABLE 4-3 above, the critical surface tension γP of thepolymer compound was 33 dyne/cm and the γP>γLC held in this Example 2-4also. Also, as seen from the results shown in TABLE 4-3 and FIG. 36, theV90%-temperature curve of Example 2-4 shows a rising higher pattern thatas temperature rose, the V90% increases, as in the case with the aboveExample 2—2, but the temperature dependency index was 0.22 of smallerthan that of the above Example 2.

Example 2-5

Except that the polymerizable monomer having hydroxyl group(Monofunctional acrylate; M-5700 available from TOAGOSEI CO., LTD.) wasused and the polymerizable oligomer having hydroxyl group (Polyesteracrylate); M-6100 available from TOAGOSEI CO., LTD.) was used as thepolymerizable oligomer, the polymer dispersion type liquid crystaldisplay element was produced in the same manner as in Example 2-1, andthe same measurements were made as in Example 2-1. The results are shownin FIG. 37 and TABLE 4-3 given above.

Result

As seen from TABLE 4-3 above, the critical surface tension γP of thepolymer compound was 32 dyne/cm and the γP>γLC held in this Example 2-5also. Also, as seen from the results shown in TABLE 4-3 and FIG. 37, theV90%-temperature curve of this Example 2-5 showed a gently curvingpattern having a minimum value at the vicinity of 30° C., while on theother hand, the temperature dependency index was as relatively small as0.25.

Example 2-6

Except that the polymerizable monomer having carboxyl group(Monofunctional acrylate; M-5400 available from TOAGOSEI CO., LTD.) wasused and the M-6100 available from TOAGOSEI CO., LTD. was used as thepolymerizable oligomer as in the case of Example 2-5, all were the sameas those in Example 2-1 above. The same measurements as those in Example1 were made. The measurement results are shown in FIG. 38 and TABLE 4-3given above.

Result

As seen from TABLE 4-3 above, the critical surface tension γP of thepolymer compound was 32 dyne/cm and the γP>γLC held in this Example 2-6also. Also, as seen from the results shown in TABLE 4-3 and FIG. 37, theV90%-temperature curve of Example 2-6 showed a similar pattern to thatof the above Example 2-5, but the temperature dependency index was 0.22of smaller than that of Example 2-5.

Comparative Example 2-1

Except that the oligomer having no polar group (1,6hexanedioldiacrylate; Biscourt #230 available from OSAKA ORGANICCHEMICAL INDUSTRY) was used, the polymer dispersion type liquid crystaldisplay element was produced in a similar manner to in the abovesaidExample 2-1, and the same measurements as those in the Example 2-1 weremade. The measurement results are shown in TABLE 4-3 above and FIG. 39.

Result

The characteristic feature of the liquid crystal display element ofComparative Example 2-1 is in that the polymer compound has no polargroup. As seen from TABLE 4-3 above, the critical surface tension γP ofthe polymer compound was 25 dyne/cm and the γP>γLC did not hold in thisComparative Example 2-1.

Also, according to this Comparative Example 2-1, V90% decreased astemperature rose, as shown in FIG. 39, and the temperature dependencyindex was as so large as 0.50. This means that since the liquid crystaldisplay element according to Comparative Example 2-1 is high intemperature dependency, the stable display cannot be presented whentemperature varies.

It can be confirmed from comparison between the results of Example 2-1through Example 2-6 and the results of Comparative Example 2-1 that whenthe γP>γLC holds between the critical surface tension γP of the polymercompound and the surface tension γLC of the liquid crystal, the liquidcrystal display element low in temperature dependency is presented. Itshould be noted that when the γP>γLC does not hold between the criticalsurface tension γP and the surface tension γLC of the liquid crystalmaterial, the temperature dependency of light transmission of the liquidcrystal display element increases, which is thought to be because theinterface polymer/liquid crystal becomes so unstable in energy that thephase transition may be caused between the bipolar form and the radialform. From this point of view, it is desirable that the relation ofγP>γLC always hold in the operating temperature range of the liquidcrystal display element.

Other Matters

Acrylate base polymerizable materials or methacrylate base polymerizablematerials are generally used in view of their having a similarrefractive index to an ordinary index of the liquid crystal to provide ahigh transmittance and their rapid polymerization reaction, though neednot be limited thereto. Epoxy base glycelinediglycidyl ether may beused, for example.

The insulating film used may also be selected from either of a polyimidetype one and a polyamic acid type one without being limited to thosedisclosed above. Also, an inorganic insulating film may be used. Theinsulating film used provides the effect of enhancing the retention ofvoltage.

Example 4-3

Example 4-3 is an example directed to the 65^(th) to 77^(th) aspects ofthe fourth inventive group.

After insulating paint films (critical surface tension γP=32.5 dyne/cm)made of poly-L-glutamic acid modified with decamethylene diamine wererespectively formed on a pair of upper and lower support substrates eachhaving an electrode, the upper and lower support substrates were bondedtogether through spacers at an interval of 13 μm, with the insulatingfilms confronting each other, to complete an empty cell. Then, 0.80 g ofliquid crystal material having a 30 dyne/cm surface tension as theliquid crystal material, 0.60 g of 2 ethylhexyl acrylate (available fromNAKARAI TESK CO., LTD.) as the polymer forming monomer, 0.39 g of M1600(available from TOAGOSEI CO., LTD.) as the oligomer material, and 0.01 gof Benzyl Dimethyl Ketal (available from NIPPON KAYAKU CO., LTD.) wereprepared and fully stirred and then were injected into the empty cell.After completion of the injection, the resultant cell was irradiatedwith ultraviolet of 365 nm (95 MW/cm²) under the temperature of 20° C.for 100 seconds, to complete the liquid crystal display element composedof polymer dispersion type liquid crystal in which liquid crystals aredispersed in the polymer matrix.

The critical surface tension of the polymer matrix was measured by thefollowing technique.

The two opposing substrates were peeled off from the liquid crystaldisplay element, and then the polymer matrix was washed with isopropylalcohol to eliminate the liquid crystals from its surface and dried byblowing nitrogen against it. Thereafter, the critical surface tensionwas determined in the Disman plotting method through the use of awettability indexing testing agent (available from NAKARAI TESK CO.,LTD.). The critical surface tension of the polymer matrix thusdetermined was 32 dyne/cm.

Next, the liquid crystal display element thus produced was measured inrespect of temperature dependency of the driving voltage with the liquidcrystal evaluation apparatus of LCD5000 available from OTSUKAELECTRONICS CO., LTD.

The temperature dependency was evaluated with the value of ΔV calculatedby Expression 6 as the index.

This index indicates that the smaller the ΔV, the better the temperaturedependency.

The liquid crystal display element produced this time presented thedriving voltages of 9.8 V under 20° C.; 9.8 V under 30° C.; and 9.7 Vunder 40° C., and it follows that ΔV is 1.02%. This shows that theliquid crystal display element with improved temperature dependency wasachieved.

ΔV=((Vmax−Vmin)/³⁰V90%)×100  Expression 4-6

Capabilities of Exploitation in Industry

As described above, according to the present invention, a liquid crystaldisplay element, in which a polymer dispersion type liquid crystal, inwhich liquid crystal droplets are dispersed and held in a continuousphase of matrix comprising polymer compound or are dispersed and held innetworks of a three dimensional network form of matrix comprisingpolymer compound, is sandwiched between a pair of substrates each havingan electrode at the inside thereof, wherein the liquid crystal dropletsare formed to be substantially identical in shape and size, withminimized variations in particle diameter, so that the liquid crystaldroplets can be stably kept in the bipolar orientation pattern within awide temperature range, to minimize hysteresis of transmittance of lightto a voltage applied across the electrodes.

Similar effects can be produced by tilt angles of liquid crystalmolecules in the vicinity of interface between the liquid crystaldroplets and the polymer compound being minimized or by anchoringstrength being increased, by adding an interfacial restrictive forcecontrolling material to a liquid crystal polymer precursor compatiblesolution or raising a temperature under which polymerization of polymersand phase separation between the polymer and the liquid crystal areperformed by irradiation of ultraviolet.

Further, similar effects can be produced by the capacitance hysteresisbeing minimized or by the ratio of capacitance for the voltage toprovide a not less than 10% transmittance of a voltage-transmittancecharacteristic being controlled to be not less than 60%.

Also, an improved response to electric field can be provided within awide operation temperature range by allowing surface tension of liquidcrystal material to be smaller than critical surface tension of aninsulating film or surface tension of the polymer compound.

Accordingly, the liquid crystal display element according to theinvention is available for forming displays, such as television sets andpersonal computers, capable of displaying moving pictures and the likewithin a wide operation temperature range, so that significance inindustry of the present invention is great.

What is claimed is:
 1. A method for producing a polymer dispersion typeliquid crystal display element in which a polymer dispersion type liquidcrystal is sandwiched between a pair of substrates each having anelectrode at the inside thereof, said polymer dispersion type liquidcrystal being such that liquid crystal droplets are dispersed and heldin a continuous phase of matrix comprising polymer compound or aredispersed and held in networks of a three dimensional network form ofmatrix comprising polymer compound, wherein a value of (V90 (volt)×R)/dis 0.7 or more, where V90 (volt) is an applied voltage required fortransmittance of a voltage.transmittance characteristic of said polymerdispersion type liquid crystal display element to become 90% under 30°C. of the temperature of element; d (μm) is an interval between saidpair of substrates; and R (μm) is an average particle size of saidliquid crystal droplets, said method comprising the step that under thecondition that said liquid crystal polymer precursor compatible solutionincluding liquid crystal and polymer precursor placed between said pairof substrates is maintained at a higher temperature than a thermal phaseseparation temperature of said liquid crystal polymer precursorcompatible solution, said liquid crystal polymer precursor compatiblesolution is irradiate with ultraviolet to allow said liquid crystal andsaid polymer precursor to be phase-separated from each other.
 2. Amethod for producing a polymer dispersion type liquid crystal displayelement as set forth in claim 1, wherein said temperature of said liquidcrystal polymer precursor compatible solution is rendered higher thansaid thermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 2 to 15° C. and also said intensity ofultraviolet irradiation is set at not less than 100 mW/cm².
 3. A methodfor producing a polymer dispersion type liquid crystal display elementas set forth in claim 1, wherein said temperature of said liquid crystalpolymer precursor compatible solution is rendered higher than saidthermal phase separation temperature of said liquid crystal polymerprecursor compatible solution by 6 to 13° C. and also said intensity ofultraviolet irradiation is set at 160 mW/cm² to 400 mW/cm².
 4. A methodfor producing a polymer dispersion type liquid crystal display elementas set forth in claim 1, wherein said liquid crystal polymer precursorcompatible solution includes monofunctional acrylate and/ormultifunctional acrylate.
 5. A method for producing a polymer dispersiontype liquid crystal display element as set forth in claim 4, whereinsaid monofunctional acrylate is isostearyl acrylate; and saidmultifunctional acrylate is at least one material selected from thegroup consisting of triethylene glycol diacrylate, polyethylene glycol(molecular weight 200) diacrylate, polyethylene glycol (molecular weight400) diacrylate, neopentyl glycol diacrylate, 1,6-hexandiol diacrylate,trimethylolpropane triacrylate, pentaerythlytoltriacrylate, andbifunctional urethane acrylate expressed by the chemical formula 1 givenbelow:CH₂═CHCOO—R′—OOCNH—(R—NHCOO-(polyol)-OOCNH)_(n)—R—NHCOO—R′—OCOCH═CH₂  Chemicalformula 1 where n=an integer.
 6. A method for producing a polymerdispersion type liquid crystal display element as set forth in claim 2,wherein said liquid crystal polymer precursor compatible solutionincludes a monofunctional acrylate, a multifunctional acrylate, ormixtures thereof.
 7. A method for producing a polymer dispersion typeliquid crystal display element as set forth in claim 3, wherein saidliquid crystal polymer precursor compatible solution includes amonofunctional acrylate, a multifunctional acrylate, or mixturesthereof.